SE1651359A1

SE1651359A1 - A method for load determination of a vehicle, a vehicle loadsensing system, a vehicle, a computer program and a compute r program product

Info

Publication number: SE1651359A1
Application number: SE1651359A
Authority: SE
Inventors: Skaba Robert
Original assignee: Scania Cv Ab
Priority date: 2016-10-18
Filing date: 2016-10-18
Publication date: 2018-04-19
Also published as: SE540329C2; DE102017009146A1

Abstract

The invention relates to a method for load determination of a vehicle (1 ), the vehicle (1) comprising a chassis (3) and a pneumatic suspension system (200) with pneumatic suspension means (201) arranged on at least one axle (6, 10), wherein the height of the chassis (3) in relation to the at least one axle (6, 10) can be changed by controlling the amount of air in the suspension means (201) and thereby changing the extension of the suspension means (201). The method comprises the step of, for each axle (6, 10): determining (s100) the load on the suspension means (201) based on the pressure in the suspension means (201), the extension of the suspension means (201), and the previous travel direction of the suspension means (201).The invention also relates to a vehicle load sensing system (100), a vehicle (1), a computer program (P) and a computer program product.

Description

A method for load determination of a vehicle, a vehicle load sensingsystem, a vehicle, a computer program and a computer program product TECHNICAL FIELD The present invention relates to a method for load determination of a vehicle, avehicle load sensing system, a vehicle comprising such a system, a computerprogram and a computer program product according to the appended claims.The invention more specifically relates to a method and a system fordetermining the load of a vehicle comprising a pneumatic suspension system.

BACKG ROUND Heavy vehicles, such as commercial vehicles, often transport cargo whichaffects the load on the vehicle axles. For a certain transport mission theoperator of a vehicle may be payed based on the amount of cargo transported.lt is therefore desired to be able to determine the vehicle load in a time efficientand accurate way. l\/lost vehicles today comprise pneumatic suspensionsystems for levelling the vehicle, where a compressor unit supplies pressurizedair into flexible bellows associated with each axle. By determining the pressurein the bellows, the load on the bellows can be estimated and the amount ofcargo on the vehicle can thereby be estimated. This method is however notvery accurate and the estimated load may differ with several hundred kilosfrom the actual load. An inaccurate load estimation may affect the payment ofthe vehicle operator and the cargo efficiency. The load on the bellows of anaxle is typically referred to as the sprung weight of the axle. The sprung weightis thus the load supported by the pneumatic suspension system, including inmost applications approximately half of the weight of the pneumaticsuspension system itself. The sprung weight may be used to determine theaxle load of a vehicle. The axle load is the total weight on the road provided by all wheels of an axle. There are legal restrictions relating to the axle load ofeach axle and it is therefore of utter importance that the axle load estimation isas accurate as possible. To determine the axle load based only on the sprungweight is not accurate since the mass of the vehicle components not supportedby the pneumatic suspension bellows is ignored.

US2002/0038193 A1determining the axle load of a vehicle. The method comprises to determine the Document discloses a device and method forextension of the bellow and based on that determine an effective cross-sectional area of the bellow. The cross-sectional area is then multiplied with adetermined pressure in the bellow to get the axle load. Document EP1571429A2 discloses a method for determining the axle load of a vehicle by using acorrection factor to compensate for that the effective bellow working area varywith the extension of the bellow. The relationship between pressure in thebellow and the load on the bellow is approximated by taking an average ofload characteristics for when the bellow is inflated and load characteristics forwhen the below is deflated. Based on the average the correction factor for thebellow effective working area is calculated.

SUMMARY OF THE INVENTION Despite known solutions in the field, there is still a need to develop animproved method and system for load determination of a vehicle.

An object of the present invention is to achieve an advantageous method forload determination of a vehicle, which improves the accuracy of a determinedsprung weight of a vehicle.

Another object of the present invention is to achieve an advantageous methodfor load determination of a vehicle, which improves the accuracy of adetermined axle load of a vehicle.

A further object of the present invention is to achieve an advantageous vehicleload sensing system associated with a pneumatic suspension system, whichimproves the accuracy of the determination of the sprung weight of a vehicle.

Another object of the present invention is to achieve an advantageous vehicleload sensing system associated with a pneumatic suspension system, whichimproves the accuracy of the determination of the axle load of a vehicle.

The herein mentioned objects are achieved by a method for load determinationof a vehicle, a vehicle load sensing system associated with a pneumaticsuspension system, a vehicle comprising such a load sensing system, acomputer program and a computer program product according to theindependent claims.

According to an aspect of the present invention a method for loaddetermination of a vehicle is provided. The vehicle comprising a chassis and apneumatic suspension system with pneumatic suspension means arranged onat least one axle, wherein the height of the chassis in relation to the at leastone axle can be changed by controlling the amount of air in the suspensionmeans and thereby changing the extension of the suspension means. Themethod comprises the step of, for each axle: - determining the load on the suspension means based on the pressure in thesuspension means, the extension of the suspension means, and the previoustravel direction of the suspension means.

The load on the suspension means is suitably determined by an algorithmtaking the pressure in the suspension means, the extension of the suspension means, and the previous travel direction of the suspension means into account.

Pneumatic suspension systems for levelling a vehicle are known to comprise acompressor unit supplying pressurized air into pneumatic suspension means associated with each axle. At least one axle of the vehicle comprises such suspension means. As an example at least one front axle and at least one rearaxle comprises such suspension means. The suspension means suitablycomprises a flexible bellow with a piston, such as for example a folding sleevebellow. The suspension means may comprise a rubber bellow. The suspensionmeans is suitably connected to an axle at one end and to the chassis at theother end. The suspension means may be connected to the axle via a link arm.When the air supply system inflates the suspension means of an axle thevehicle chassis is raised from that axle. Similarly, when the amount of air ormass of air inside the suspension means is decreased, the suspension meansis deflated and the vehicle chassis is lowered towards the axle. lt is commonlyknown that a certain pressure in the suspension means corresponds to acertain load on the suspension means. The weight of the load on thesuspension means is considered to be equal to the pressure in the suspensionmeans multiplied with the effective area of the suspension means. However,the effective area changes as the suspension means is extended and retracteddue to the configuration of the suspension means. The relationship betweenthe pressure and the load thus vary depending on the extension of thesuspension means and thus the chassis height. Depending on the type ofsuspension means the effective area may change due to a piston shape,changes in the angle between the piston and the longitudinal axis of thesuspension means or just due to the changes in the form/shape of the rubberas the suspension means is extended or contracted. Furthermore, dependingon the extension of the suspension means the geometry of the suspensionaffects the relationship between the pressure and the load. The geometry ofthe suspension, for example how the suspension means is connected to thelink arm, determines how the force from the suspension means acts to raisethe chassis. The direction of the force from the suspension means thuschanges as the suspension means is extracted or retracted and more or lessair mass is required to support the chassis. To be able to determine the loadon the suspension means in an accurate way it is therefore an advantage to take into account the extension of the suspension means.

The relationship between the pressure and the load also vary depending onthe previous travel direction of the suspension means. By previous traveldirection is meant whether the suspension means was inflated/extended ordeflated/retracted just before the load determination. When the chassis israised and the suspension means is extended, the suspension means has toovercome suspension friction, air bellow internal friction mechanisms andtorques coming from suspension bushings. When the chassis is lowered andthe suspension means is retraced, friction acts to take the load off thesuspension means. The internal friction mechanisms of the suspension meansalso help to support the chassis. The folding action that happens when thesuspension means is retracted also requires energy and force since the bellowrubber is being compressed and therefore takes the load off the suspensionmeans. The suspension bushings have hysteresis which means that they exerta higher force, at the same chassis height, if the chassis previously has beenraised than if the chassis previously has been lowered. The previous traveldirection of the suspension means thus clearly affects the relationship betweenthe pressure and the load. By determining the load on the suspension meansbased not only on the pressure in the suspension means but also based on theextension of the suspension means and the previous travel direction of thesuspension means a more accurate determination of the load on thesuspension means is achieved.

The load on the suspension means may be referred to as bellow load or somefraction of the sprung weight. The fraction depends on the suspension meansgeometry. The sprung weight typically includes the mass of everything abovethe suspension means, such as the chassis, passengers, cargo etc. Thesprung weight may also include part of the mass of the suspension systemitself. The unsprung weight of a vehicle is the mass of the componentssomewhat connected to the suspension means rather than supported by thesuspension means. The unsprung weight thus includes for example the massof the wheels, the axle, the tires, part of the suspension system and if it is thedrive axle, the final drive and part of the mass of the driveshaft. By adding the unsprung weight of an axle to the sprung weight acting on an axle the axleload is achieved. The axle load is thus the total weight on the road providedthrough the wheels of an axle. ln other words, the axle load is the part of thetotal vehicle weight carried by a certain axle. Legal requirements restrict themaximum axle load allowed in order not to damage the road.

According to an aspect of the invention the method comprises the steps of: - determining the pressure in the suspension means; - determining the extension of the suspension means; - determining the previous travel direction of the suspension means; and - determining the load on the suspension means based on the determinedpressure, extension and travel direction.

According to an aspect of the invention the method comprises the steps of: - determining the pressure in the suspension means; - determining the extension of the suspension means; - determining the previous travel direction of the suspension means; and - determining the load on the suspension means based on the determinedpressure, extension and travel direction and based on a predeterminedrelationship between the load on the suspension means, the pressure in thesuspension means and the extension of the suspension means, wherein therelationship depends on the previous travel direction of the suspension means.

The predetermined relationship is suitably different for suspension means ondifferent axles. Thus, there may be a different predetermined relationship foreach axle on the vehicle. The relationship may be different for different axlesdue to different configuration of the suspension means on the different axles.

An operator of the vehicle suitably activates the load determination methodmanually by operation of a load determination control means, such as a buttonor lever or similar. Upon operation of the load determination control means a signal is suitably transmitted to a vehicle load sensing system which initiates execution of the load determination method. The load sensing system thusdetermines the current pressure in the suspension means of each axle, thecurrent extension of the suspension means of each axle and the previoustravel direction of the suspension means of each axel. This data is suitablyinput to an algorithm in a control unit of the load sensing system, this controlunit stores the predetermined relationship between the load on the suspensionmeans, the pressure in the suspension means and the extension of thesuspension means. Based on the input data and the predeterminedrelationship the current load on the suspension means can be determined.Since there are two different travel directions, upwards and downwards, thecontrol unit suitably comprises two different load-pressure-extensionrelationships. There is thus one relationship between load, pressure andextension if the suspension means has previously been extended and anotherrelationship between load, pressure and extension if the suspension meanshas previously been retracted. lt is to be understood that by relationship ismeant a mathematical relationship. When the load sensing system hasdetermined the load on the suspension means of all axles of the vehicle, the result is suitably schematically presented on a display unit in the vehicle.

The relationship between the load on the suspension means, the pressure inthe suspension means and the extension of the suspension means for a traveldirection upwards is suitably compiled in a first three dimensional curve andthe relationship between the load on the suspension means, the pressure inthe suspension means and the extension of the suspension means for a traveldirection downwards is suitably compiled in a second three dimensional curve.The control unit thus suitably stores two three dimensional curves showing thetwo different relationships. The three dimensional curves may also be referredto as three dimensional graphs or diagrams. The method thus suitablycomprises to determine the load on the suspension means based on a firstthree dimensional curve of the relationship between the load on thesuspension means, the pressure in the suspension means and the extension of the suspension means for a previous travel direction upwards or a second three dimensional curve of the relationship between the load on thesuspension means, the pressure in the suspension means and the extensionof the suspension means for a previous travel direction downwards.Depending on the determined previous travel direction one of thecurves/relationships is used to determine the load on the suspension meansbased on the determined pressure and extension. The algorithm is thusrealized with two three dimensional curves, for each axle of the vehicle. Thepressure in the suspension means and the extension of the suspension meansare suitably independent variables and the load on the suspension means issuitably the dependent variable. The pressure in the suspension means andthe extension of the suspension means are suitably presented on the x and yaxis and the load on the suspension means is suitably presented on the z axis.Each relationship between pressure, extension and load is suitably empiricallydetermined. Suitably, the pressure in the suspension means and the load onthe suspension means are determined for certain extensions of the suspensionmeans, the extensions being spaced at regular intervals, for example 1, 5 and10 millimetres. Each relationship is thus determined by experiments. This way,calculation of the effective area of the suspension means is avoided.

Relationships are suitably determined for each type of suspension means.

According to an aspect of the invention the extension of the suspension meansof an axle is determined by means of a chassis height sensor arranged inassociation with that axle. The extension of the suspension means may thusbe referred to as chassis height.

According to an aspect of the invention the extension of the suspension meansof an axle is derived from the chassis height in relation to the other axles of thevehicle. Sometimes not all axles of a vehicle comprise a chassis height sensor.For example, when the vehicle comprises two or more rear axles the tagaxle(s) (not driven axle) may not comprise a chassis height sensor. Preferablyonly the front axle and the drive axle of a vehicle comprise chassis heightsensors. ln this case the extension of the suspension means on the tag axle can be calculated based on the chassis height at the front axle and the driveaxle. The extension of the suspension means may also be calculated based onthe axle to axle distances together with the determined chassis height at thefront axle and the drive axle.

The previous travel direction of the suspension means is suitably determinedby means of the chassis height sensor and/or whether air has previously been led in to the suspension means or out of them.

According to an aspect of the invention the load on the suspension means ofeach axle is further determined based on the vehicle pitch angle. The vehiclepitch angle is the angle between the longitudinal axis of the vehicle and theground plane. The vehicle pitch angle is suitably determined by determiningthe chassis height at the at least one front axle of the vehicle and at the atleast one rear axle of the vehicle. The vehicle pitch angle may thus indicate ifthe vehicle chassis (i.e. frame) is essentially level with the ground plane basedon the distance from the front axle and the distance from the rear axle. Thevehicle pitch angle thus indicates if the chassis is tilted forwards or backwards.Whether the chassis is tilted or not affects the load distribution between thedifferent suspension means and further changes the air bellow pressure toaxle load relationship per given chassis height depending on the airsuspension means geometry. By determining the load on the suspensionmeans of each axle based on the vehicle pitch angle, a more accurate loaddetermination is achieved.

According to an aspect of the invention the load on the suspension means ofeach axle is further determined based on the road slope. The road slope mayalso be referred to as the road gradient and is the inclination of the road inrelation to the horizontal axis. Typically, when the load is determined thevehicle wheels are braked by service brakes and/or parking brakes. The roadslope affects the pressure to load relationship for the axles with braked wheelsdue to the torque acting on the link arm connecting the suspension means and the braked road wheel. This torque does not normally exist while on levelground and the vehicle braked. This torque is proportional to the pressure ofeach suspension means, and therefore its relative magnitudes amongst thedifferent suspension means are known. The sum of these torques ismathematically related to the total vehicle weight and road slope and therebythe link arm torque for each suspension means can be calculated if the totalvehicle weight is known. This leads to an actual road slope correction factor.The vehicle weight may be determined from the load sensing system when thevehicle was on level ground, or from other systems. The road slope may bedetermined by means of a chassis height sensor at a front axle and a chassisheight sensor at a rear axle in combination with an acceleration sensorarranged at the vehicle chassis. By determining the load on the suspensionmeans of each axle based on the road slope, a more accurate loaddetermination is achieved.

The vehicle pitch angle and the road slope may be combined to a correctionfactor and be multiplied with the load on the suspension means determinedbased on the pressure in the suspension means, the extension of the suspension means and the previous travel direction of the suspension means.

According to an aspect of the invention the method further comprises the stepsof: - determining the unsprung weight associated with each axle; and - determining the axle load for each axle by adding the unsprung weight to thedetermined load on the suspension means.

As previously described the unsprung weight is essentially the mass of thecomponents connected to the suspension means but not supported by thesuspension means. lt is difficult to determine the unsprung weight and it istherefore often neglected when estimating the axle load of a vehicle. Bydetermining the unsprung weight of each axle and adding it to the load on thesuspension means determined for each axle, an accurate value of the axle 11 load is achieved. Thus, an accurate and efficient way of determining the axleload of a vehicle is thereby achieved. The unsprung weight of all axles of thevehicle is suitably predetermined and stored in the vehicle load sensingsystem.

The unsprung weight of an axle may be determined by measurement bymeans of a scale weighing machine. This is only possible when the axle isarranged next to another axle. The step of determining the unsprung weight ofa first axle arranged adjacent to a second axle may comprise to exhaust the airin the suspension means of the first axle and at the same time add air(pressure) to the suspension means of the second axle. This way, the secondaxle can carry the load previously carried by the first axle and it is ensured thatthe chassis height is not changed. The first axle is then lifted by the vehiclesown axle lift bellow and the vehicle is operated to a position where the first axlecan be lowered onto a scales. Alternatively, a scale weighing machine isarranged underneath the lifted first axle. The first axle is then lowered onto thescale weighing machine and the unsprung weight of the first axle can therebybe measured. Alternatively, the vehicle is operated such that the first axle ispositioned on a scale weighing machine, whereafter the air in the suspensionmeans of the first axle is exhausted and at the same time air is added to thesuspension means of the second axle. The unsprung weight for each axle issuitably stored in the vehicle load sensing system, such that it can be used fordetermining the axle load of the vehicle.

Alternatively, the unsprung weight of an axle may be determined by a pressureto load correlation when the axle is lifted. The step of determining theunsprung weight may thus comprise to lift the axle by means of a lift bellowand determine the pressure in the lift bellow. A known relationship between thepressure in the lift bellow and the load lifted by the lift bellow is then used toestimate the unsprung weight of the axle. 12 According to an aspect of the invention the method comprises to calibrate therelationship between pressure in the suspension means, extension of thesuspension means and the load on the suspension means. An algorithmsuitably allows the vehicle owner or operator of the vehicle to calibrate thepredetermined relationship between pressure in the suspension means,extension of the suspension means and the load on the suspension means, foreach axle. The algorithm suitably allows the vehicle owner or operator of thevehicle to calibrate the vehicle load sensing system. The calibration comprisesto operate the vehicle such that an axle is positioned on a scale weighingmachine. A first load is suitably placed on the vehicle and the weight on theaxle is determined by means of the scales. The pressure in the suspensionmeans on the axle is then determined by conventional pressure sensorsarranged in association with the suspension means. More load is subsequentlyplaced on the vehicle and the weight and pressure is once again determined.This may be repeated with more loads in order to achieve a more reliablerelationship between load and pressure. This is suitably repeated for all axlesof the vehicle. The predetermined relationship is then compared with themeasured relationship. The calibration may be manually activated by theoperator. The calibration may be activated by the operator manually operatinga calibration control means such as a button, lever or similar. When thecalibration is activated instructions on how to proceed to perform thecalibration is suitably presented to the operator on a display unit in the vehicle.The operator is suitably instructed to input the weight into the load sensingsystem via input means, such as a touch screen, buttons or similar. This way,a time efficient and easy way of calibrating the load sensing system isachieved.

According to an aspect of the invention a vehicle load sensing systemassociated with a pneumatic suspension system is provided. The pneumaticsuspension system comprising pneumatic suspension means arranged on atleast one axle, wherein the height of a vehicle chassis in relation to the at leastone axle is adapted to be changed by controlling the amount of air in the 13 suspension means and thereby changing the extension of the suspensionmeans. The vehicle load sensing system comprises a control unit adapted to,for each axle, determine the load on the suspension means based on thepressure in the suspension means, the extension of the suspension means,and the previous travel direction of the suspension means.

The control unit is suitably adapted to determine the pressure in thesuspension means; determine the extension of the suspension means;determine the previous travel direction of the suspension means; and todetermine the load on the suspension means based on the determinedpressure, extension and travel direction. The control unit is suitably adapted todetermine the pressure in the suspension means; determine the extension ofthe suspension means; determine the previous travel direction of thesuspension means; and to determine the load on the suspension means basedon the determined pressure, extension and travel direction and based on apredetermined relationship between the load on the suspension means, thepressure in the suspension means and the extension of the suspension means,wherein the relationship depends on the determined previous travel directionof the suspension means. The control unit is suitably arranged incommunication with a load determination control means for activation of theload determination. When such load determination control means is operated asignal is transmitted to the control unit of the load sensing system whichinitiates the load determination process. The control unit suitably comprises analgorithm taking the pressure in the suspension means, the extension of thesuspension means, and the previous travel direction of the suspension means into consideration when determining the load on the suspension means.

The relationship between the load on the suspension means, the pressure inthe suspension means and the extension of the suspension means for a traveldirection upwards is suitably compiled in a first three dimensional curve in thecontrol unit and a relationship between the load on the suspension means, the pressure in the suspension means and the extension of the suspension means 14 for a travel direction downwards is suitably compiled in a second threedimensional curve in the control unit. The control unit thus comprises a firstthree dimensional curve showing the relationship between the pressure in thesuspension means, the extension of the suspension means and the load onthe suspension means for the case when the previous travel direction of thesuspension means was upwards. The control unit also comprises a secondthree dimensional curve showing the relationship between the pressure in thesuspension means, the extension of the suspension means and the load onthe suspension means for the case when the previous travel direction of thesuspension means was downwards.

According to an aspect of the invention the control unit is adapted to determinethe extension of the suspension means by means of a chassis height sensorarranged in association with that axle. The control unit is suitably arranged incommunication with a chassis height sensor arranged in association with anaxle. The control unit is thus adapted to receive a signal from the chassisheight sensor indicating the distance between the chassis and the axle.Alternatively, the control unit is adapted to determine the extension of thesuspension means by calculation based on the chassis height at the otheraxles of the vehicle. ln the case where the axle does not have a chassis heightsensor the extension of the suspension means can be derived from thedetermined chassis height at the other axles. The control unit may be adaptedto determine the extension of the suspension means of an axle by calculationbased on the chassis height at the other axles of the vehicle and the distancesbetween the axles.

According to an aspect of the invention the control unit is adapted to determinethe load on the suspension means of each axle further based on the vehiclepitch angle. The control unit is suitably arranged in communication with chassisheight sensors arranged at a front axle and a rear axle. The control unit is thusadapted to receive chassis height signals from the chassis height sensors andbased on those signals determine the vehicle pitch angle. The control unit may also be adapted to determine the load on the suspension means of each axle based on the road slope. The control unit is suitably arranged incommunication with chassis height sensors arranged at a front axle and a rearaxle and with an acceleration sensor. The control unit is thus adapted toreceive signals from the chassis height sensors and the acceleration sensorand based on those signals determine the road slope. The control unit mayalso be adapted to combine the vehicle pitch angle and the road slope to acorrection factor and to multiply the correction factor with the load on thesuspension means determined based on the pressure in the suspensionmeans, the extension of the suspension means and the previous travel direction of the suspension means.

According to an aspect of the invention the control unit is adapted to determinethe unsprung weight associated with each axle; and to determine the axle loadfor each axle by adding the unsprung weight to the determined load on thesuspension means. The control unit may be adapted to determine theunsprung weight based on the pressure in a lift bellow when the axle is lifted.The unsprung weight for each axle of the vehicle may be predetermined andstored in the control unit, such that the control unit can determine the unsprungweight for a specific axle and determine the axle load for that specific axle.

The control unit is suitably adapted to present the determined load on thesuspension means for each axle on a display unit in the vehicle. The controlunit is suitably adapted to present the determined axle load of the vehicle on adisplay unit in the vehicle. The control unit may be adapted to present thedetermined axle load on a schematic illustration of the vehicle such that it iseasy to see the axle load on each axle of the vehicle.

According to an aspect of the invention the control unit comprises an algorithmadapted to allow the vehicle owner or operator of the vehicle to calibrate therelationship between pressure in the suspension means, extension of thesuspension means and the load on the suspension means, for each axle. The 16 control unit suitably comprises an algorithm adapted to allow the vehicle owneror operator of the vehicle to calibrate the load sensing system. The loadsensing system suitably comprises calibration control means arranged incommunication with the control unit. The control unit is thus adapted to receivea signal from the calibration control means indicating that the operator wants tostart the calibration. The control unit is adapted to present instructions on howto proceed with the calibration on a display unit when the calibration has beenactivated. The calibration includes operating the vehicle such that an axle ispositioned on a scale weighing machine. A first load is suitably placed on thevehicle and the weight is determined by means of the scales. The control unitis adapted to instruct the operator to input the weight into the load sensingsystem via input means, such as a touch screen, buttons or similar. Thepressure in the suspension means on the axle is determined by conventionalpressure sensors arranged in association with the suspension means and thecontrol unit. The control unit is thus adapted to determine the pressure in thesuspension means during calibration. More load is subsequently placed on thevehicle and the weight and pressure is once again determined. This may berepeated with more loads in order to achieve a more reliable relationshipbetween load and pressure. The control unit is adapted to compare thepredetermined relationship with the measured relationship.

Further objects, advantages and novel features of the present invention willbecome apparent to one skilled in the art from the following details, and alsoby putting the invention into practice. Whereas the invention is describedbelow, it should be noted that it is not restricted to the specific detailsdescribed. Specialists having access to the teachings herein will recognisefurther applications, modifications and incorporations within other fields, whichare within the scope of the invention. 17 BFIIEF DESCRIPTION OF THE DFIAWINGS For fuller understanding of the present invention and further objects andadvantages of it, the detailed description set out below should be read togetherwith the accompanying drawings, in which the same reference notationsdenote similar items in the various drawings, and in which: Figure 1 schematically illustrates a vehicle according to an embodiment ofthe invention; Figure 2 schematically illustrates a vehicle load sensing system accordingto an embodiment of the invention; Figure 3a schematically illustrates the relationship between pressure,extension, load and travel direction according to an embodiment ofthe invention; Figure 3b schematically illustrates the relationship between pressure, extension, load and travel direction according to an embodiment ofthe invention;Figure 4a-b schematically illustrate a flow charts for a method for loaddetermination according to an embodiment of the invention; andFigure 5 schematically illustrates a control unit or computer according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS The term “link” herein refers to a communication link which may be a physicalconnection such as an opto-electronic communication line, or a non-physicalconnection such as a wireless connection, e.g. a radio link or microwave link.Herein provided links are illustrated as being arranged for bi-directionalcommunication. However, in some cases communication between units viasuch a link may be one-directional. 18 Figure 'i scheniaticaiiy shows a siole view oi a vehioie 1 accoroing to anembodiment oi the invenrion. The vehicie 1 comprises a chassis 3, apropuision unit 2 and a gearbox 4 connected to the propuision unit 2. Thevehicie 1 further oornprises at ieast one front axie 6 with front vvheeis 8 and atieast one rear axie 10 iivith rear vvheeis 12. in this figure the vehioie 1contprises tive rear axles 10 where at ieast one ot the rear axies is a oriveaxle. The at ieast one drive axie 10 is thus connected to the gearbox 4 and thepropuision unit 2. The tfehicie 1 also coniprises a load sensirig system 100associated ilvith a pneurnatio suspension systern 200. The pnetrinaticsuspension systern 200 ior ieveiiing the vehicie 1 coinprises a corripressor unit(hot shown) suppiyiiig oressurized air into pneumatic suspension means 201associated with at ieast one axie 6, 10. in this figure aii axies 6, 10 coinprisessuspension means 201, itovifever, it is to he understooci that oniy the rear axiesrnay comprise suspension means. The pneumatio suspension means 201 aresuitabiy iiexioie oeiiows 201. The figure aiso shows a more oetaiied view oi anaxie 10 and how the suspension means 201 is arrangeci at the axie 10. Eventhough this shows a rear axie 10, the oetaiieo view is vaiid tor a ironi axie 6 asweii. The suspension means 201 suitaioiy cornprises a piston 202 nioveloiyarrangera in the ioeiiow, vvhere the piston 202 is attacheo to a link arm 203. Theother errol oi the suspension means 201 is attached to a frame 204 oi thechassis 3. By increasing the amount ot air inside the suspension means 201 oien axie 6, 10 the suspension means 201 iniiates and the chassis 3 oi thevehicie 1 is raised from the axie 6, 10. By exhaiistiitg the air inside thesuspension means 201 oi an axle 6, 10 to atrriosohere, the suspension means201 oeiiates and the chassis 3 is iovvered towards the axie 6, 10. The ioaoisensing system 100 is arrangera to determine the ioao on the suspensionmeans 201 oi each axie 6, 10 and the axle ioao oi each axie 0, 10 by rneans oithe pneuntatic suspension systern 200. The vehicle 1 may be a heavy vehicle,e.g. a truck, a bus, a forest machine, a mining vehicle, a construction vehicle, arescue vehicle, a refuse collection vehicle or similar. The vehicle 1 may be ahybrid vehicle comprising two propulsion units 2, namely an electric machine 19 and a combustion engine. The load sensing system 100 in the vehicle 1 will befurther described in Figure 2.

Figure 2 schematically illustrates a vehicle load sensing system 100associated with a pneumatic suspension system 200 of a vehicle according toan embodiment of the invention. The pneumatic suspension system 200 andthe vehicle with which the load sensing system 100 is associated may be thevehicle 1 and the pneumatic suspension system 200 as disclosed in Figure 1.The pneumatic suspension system 200 may thus comprises pneumaticsuspension means 201 arranged on at least one axle 6, 10, wherein the heightof a vehicle chassis 3 in relation to the at least one axle 6, 10 can be changedby controlling the amount of air in the suspension means 201 and therebychanging the extension of the suspension means 201. The vehicle loadsensing system 100 comprises a control unit 120 adapted to, for each axle 6,10, determine the load on the suspension means 201 based on the pressure inthe suspension means 201, the extension of the suspension means 201, andthe previous travel direction of the suspension means 201. The control unit120 suitably comprises an algorithm for load determination based on thepressure in the suspension means 201, the extension of the suspensionmeans 201, and the previous travel direction of the suspension means 201.

The control unit 120 is suitably adapted to determine the pressure in thesuspension means 201, determine the extension of the suspension means 201,determine the previous travel direction of the suspension means 201, anddetermine the load on the suspension means 201 based on the determinedpressure, extension and travel direction and based on a predeterminedrelationship between the load on the suspension means 201, the pressure inthe suspension means 201 and the extension of the suspension means201,wherein the relationship depends on the previous travel direction of thesuspension means 201. The predetermined relationship is suitably stored inthe control unit 120. The control unit 120 suitably stores two relationships peraxle 6, 10, one for a previous travel direction upwards and one for a previous travel direction downwards. The two relationships are suitably compiled in twothree dimensional graphs each showing a predetermined relationship betweenthe load on the suspension means 201, the pressure in the suspension means201, the extension of the suspension means 201, and the previous traveldirection of the suspension means 201. These graphs are illustrated in Figures3a and 3b. The control unit 120 is thus adapted to determine the currentpressure in the suspension means 201, determine the current extension of thesuspension means 201 and determine the previous travel direction of thesuspension means 201, and based on the determined travel direction use oneof the three dimensional curves to determine the load on the suspensionmeans 201 by means of the determined pressure and extension.

The control unit 120 is arranged in communication with the pneumaticsuspension system 200 via a link L200. The control unit 120 is thus adapted toreceive information from the pneumatic suspension system 200. A computer130 may be arranged for communication with the control unit 120 via a linkL130. The computer 130 may be detachably connected to the control unit 120.The computer 130 may be arranged external to the vehicle 100. The computer130 may be used to cross-load software to the control unit 120.

The load sensing system 100 suitably comprises a load determination controlmeans 140 arranged for communication with the control unit 120 via a linkL140. Hereby an operator of the vehicle 1 may manually operate said loaddetermination control means 140 for activating the load sensing system 100.The load determination control means 140 is thus suitably arranged in thevehicle cab and may be a lever, a push button or similar.

The load sensing system 100 may comprise a calibration control means 150arranged for communication with the control unit 120 via a link L150. Herebyan operator of the vehicle 1 may manually operate said calibration controlmeans 150 for activating a calibration function of the load sensing system 100.The calibration control means 150 is thus suitably arranged in the vehicle cab 21 and may be a lever, a push button or similar. The control unit 120 is suitablyadapted to present instructions on how to proceed with the calibration whenthe calibration control means 150 has been operated. The control unit 120 issuitably adapted to present instructions on a display unit of the vehicle 1.

Figure 3a and 3b shows graphs of relationships between pressure P in asuspension means, extension X of a suspension means, load L on asuspension means and previous travel direction of a suspension meansaccording to an embodiment of the invention. The suspension means issuitably the suspension means 201 as disclosed in Figure 1. Figure 3a showsa relationship between the pressure P in the suspension means, the extensionX of the suspension means and the load L on the suspension means, whenthe previous travel direction was upwards. Figure 3b shows a relationshipbetween the pressure P in the suspension means, the extension X of thesuspension means and the load L on the suspension means, when theprevious travel direction was downwards. The two three dimensional graphsare suitably used in a vehicle load sensing system 100 as disclosed in Figures1 and 2 for load determination. ln the relationships, the pressure P in the suspension means 201 and theextension X of the suspension means 201 are independent variables and theload L on the suspension means 201 or the sprung weight is the dependentvariable. The two relationships between pressure P, extension X and load Lare suitably determined by experiments. The pressure P in the suspensionmeans 201 and the load L on the suspension means 201 are determined forcertain extensions X of the suspension means 201, the extensions X beingspaced at regular intervals, for example 1, 5 and 10 millimetres.

Figure 4a schematically illustrates a flow chart of a method for loaddetermination of a vehicle according to an embodiment of the invention. Thevehicle is suitably configured as described in Figure 1. Said vehicle 1comprises a chassis 3 and a pneumatic suspension system 200 with 22 pneumatic suspension means 201 arranged on at least one axle 6, 10,wherein the height of the chassis in relation to the at least one axle 6, 10 canbe changed by controlling the amount of air in the suspension means 201 andthereby changing the extension of the suspension means 201. The methodcomprises the step of, for each axle 6, 10, determining s100 the load on thesuspension means 201 based on the pressure in the suspension means 201,the extension of the suspension means 201, and the previous travel directionof the suspension means 201. The method step is suitabiy performed bymeans of a control unit 120 of the vehicle load sensing system 100 asdisciosed in Figure 2.

Figure 4b schematically illustrates a flow chart of a method for loaddetermination of a vehicle according to an embodiment of the invention. Thevehicle is suitably configured as described in Figure 1. Said vehicle 1comprises a chassis and a pneumatic suspension system 200 with pneumaticsuspension 201 means arranged on at least one axle 6, 10, wherein the heightof the chassis in relation to the at least one axle 6, 10 can be changed bycontrolling the amount of air in the suspension means 201 and therebychanging the extension of the suspension means 201. The method comprisesthe step of, for each axle 6, 10, determining s101 the pressure in thesuspension means 201; determining s102 the extension of the suspensionmeans 201; determining s103 the previous travel direction of the suspensionmeans 201; and determining s104 the load on the suspension means 201based on the determined data and a predetermined relationship between theload on the suspension means 201, the pressure in the suspension means 201and the extension of the suspension means 201, wherein the relationshipdepends on the previous travel direction of the suspension means 201.

The load determination method is suitably manually activated by an operator ofa vehicle 1. The operator suitably operates a load determination control means,such as a lever or button, whereby a control unit of a vehicle load sensingsystem is activated and executes the method. The load sensing system is 23 suitably the load sensing system 100 as disclosed in Figure 2. The methodmay thus comprise the step of first identifying a request for load determination.Upon activation of the load determination the vehicle load sensing system 100is activated to determine the current pressure in the suspension means 201 ofeach axle 6, 10, the current extension of the suspension means 210 of eachaxle 6, 10 and the previous travel direction of the suspension means 201 ofeach axel 6, 10. This data is suitably input to an algorithm in the control unit120 of the load sensing system 100. The control unit 120 stores thepredetermined relationship between the load on the suspension means 201,the pressure in the suspension means 201 and the extension of thesuspension means 201. Based on the input data and the predeterminedrelationship the load on the suspension means 201 can be determined. Thecontrol unit 120 suitably comprises two different relationships, one for traveldirection upwards and one for travel direction downwards. There is thus onerelationship between load, pressure and extension if the suspension means201 has previously been extended and another relationship between load,pressure and extension if the suspension means 201 has previously beenretracted. When the load sensing system 100 has determined the load on thesuspension means 201 of all axles 6, 10 of the vehicle 1, the result is suitablyschematically presented on a display unit in the vehicle 1.

The step of determining s104 the load on the suspension means 201 suitablyincludes a first three dimensional curve showing the relationship between theload on the suspension means 201, the pressure in the suspension means 201and the extension of the suspension means 201 for a travel direction upwardsand a second three dimensional curve showing the relationship between theload on the suspension means 201, the pressure in the suspension means 201and the extension of the suspension means 201 for a travel directiondownwards. The control unit 120 thus suitably stores two three dimensionalcurves showing the two different relationships. These curves are shown inFigure 3a and 3b. The three dimensional curves may also be referred to asthree dimensional graphs or diagrams. The step s104 of determining the load 24 on the suspension means 201 thus suitably comprises to determine the loadon the suspension means 201 based on a first three dimensional curve of therelationship between the load on the suspension means 201, the pressure inthe suspension means 201 and the extension of the suspension means 201 fora travel direction upwards or a second three dimensional curve of therelationship between the load on the suspension means 201, the pressure inthe suspension means 201 and the extension of the suspension means 201 fora travel direction downwards. Depending on the determined previous traveldirection one of the curves/relationships is used to determine the load on thesuspension means 201 based on the determined pressure and extension.Each relationship/curve relating to the pressure, the extension and the loadhas suitably been empirically determined.

The step of determining s102 the extension of the suspension means 201 issuitably performed by means of a chassis height sensor arranged inassociation with that axle 6, 10. The chassis height sensor is suitably arrangedin communication with the control unit 120 of the load sensing system 100whereby the control unit 120 receives a signal from the chassis height sensorindicating the chassis height and thus the extension of the suspension means201. The control unit 120 thereby determines the extension of the suspensionmeans 201.

The step of determining s102 the extension of the suspension means 201 ofan axle 6, 10 may alternatively comprise to derive the extension of thesuspension means 201 from the determined chassis height at the other axles 6,10. The extension of the suspension means 201 may also be calculated basedon the distances in between the axles of the vehicle 1. Not all axles 6, 10 of avehicle 1 may comprise a chassis height sensor. For example, a tag axle maynot comprise a chassis height sensor. The extension of the suspension meanson an axle 6, 10 not having a chassis height sensor may thus be calculatedbased on the chassis height at the other axles 6, 10 of the vehicle 1. Thecontrol unit 120 of the load sensing system 100 suitably calculates the extension of the suspension means 201 based on the chassis height at theother axles 6, 10 of the vehicle 1.

The step of determining s104 the load on the suspension means 201 maycomprise to determine the load further based on the vehicle pitch angle. Thevehicle pitch angle is the angle between the longitudinal axis of the vehicle 1and the ground plane. The vehicle pitch angle may be determined bydetermining the chassis height at the at least one front axle 6 of the vehicle 1and at the at least one rear axle 10 of the vehicle 1. The control unit 120suitably determines the chassis height at the at least one front axle 6 and theat least one rear axle 10 by means of chassis height sensors. The control unit120 thereafter determines the vehicle pitch angle based on the determinedchassis height at the at least one front axle 6 and the at least one rear axle 10.

The step of determining s104 the load on the suspension means 201 maycomprise to determine the load further based on the road slope. The roadslope may also be referred to as the road gradient and is the inclination of theroad in relation to the horizontal axis. The road slope may be determined bymeans of a chassis height sensor at a front axle 6 and a chassis height sensorat a rear axle 10. The road slope may also be determined by means of anacceleration sensor arranged at the vehicle chassis 3 and the chassis heightsensors situated at the front axle and the rear axle. Suitably, the pitch angle ofthe vehicle 1 is used to determine the road slope. The control unit 120 of theload sensing system 100 is suitably arranged in communication with thechassis height sensors and the acceleration sensors. The control unit 120 thusreceives data from the height sensors and from the acceleration sensors anduses that data to determine the road slope.

The step of determining s104 the load on the suspension means 201 maycomprise to combine the vehicle pitch angle and the road slope to a correctionfactor and multiply it with the load on the suspension means 201 determinedbased on the pressure in the suspension means 201, the extension of the 26 suspension means 201 and the previous travel direction of the suspensionmeans 201. The control unit 120 suitably determines the vehicle pitch angleand the road slope and combines them to a correction factor. The control unit120 then multiplies this correction factor to the load on the suspension means201 determined by means of the predetermined relationship between thepressure, the extension and the travel direction of the suspension means 201.

The method may further comprise the steps of determining the unsprungweight associated with each axle 6, 10; and determining the axle load for eachaxle 6, 10 by adding the unsprung weight to the determined load on thesuspension means 201. The unsprung weight is essentially the mass of thecomponents somewhat connected to the suspension means 201 but notsupported by the suspension means 201. By determining the unsprung weightof each axle 6, 10 and adding it to the load on the suspension means 201determined for each axle 6, 10, an accurate value of the axle load is achieved.The unsprung weight is suitably stored in the control unit 120. The unsprungweight of an axle may be determined by measurement by means of a scaleweighing machine. This is only possible when the axle 6, 10 is arranged nextto another axle 6, 10. The step of determining the unsprung weight of a firstaxle 6, 10 arranged adjacent to a second axle 6, 10 may comprise to removethe pressure in the suspension means 201 of the first axle 6, 10 and at thesame time add pressure to the suspension means 201 of the second axle 6,10. This way, the second axle 6, 10 can carry the load previously carried bythe first axle 6, 10 and it is ensured that the chassis height is not changed. Thefirst axle 6, 10 is then lifted by the vehicle's own axle lift bellow and the vehicle1 is operated to a position where the first axle 6, 10 can be lowered onto ascales. Alternatively, a scale weighing machine is arranged underneath thelifted first axle 6, 10. The first axle 6, 10 is then lowered onto the scaleweighing machine and the unsprung weight of the first axle 6, 10 can therebybe measured. Alternatively, the vehicle 1 is operated such that the first axle 6,10 is positioned on a scale weighing machine, whereafter the pressure in thesuspension means 201 of the first axle 6, 10 is removed and at the same time 27 pressure is added to the suspension means 201 of the second axle 6, 10. Thecontrol unit 120 of the load sensing system 100 suitably removes the pressurein the suspension means 201 of the relevant axle 6, 10 and adds pressure tothe adjacent axle 6, 10. The control unit 120 also presents instructions to theoperator of the vehicle 1 to input the weight shown on the scale weighingmachine into the load sensing system 100. This way, the control unit 120 candetermine the unsprung weight and adds the unsprung weight to the alreadydetermined load on the suspension means 201. The control unit 120 thusdetermines the axle load.

Alternatively, the unsprung weight of an axle 6, 10 may be determined by apressure to load correlation when the axle 6, 10 is lifted. The step ofdetermining the unsprung weight may thus comprise to lift the axle 6, 10 bymeans of a lift bellow and determine the pressure in the lift bellow. The controlunit 120 is suitably arranged in communication with a pressure sensorarranged in association with the lift bellow. The control unit 120 therebydetermines the pressure in the lift bellow. A known relationship between thepressure in the lift bellow and the load lifted by the lift bellow is stored in thecontrol unit 120 and the control unit 120 suitably uses this relationship and thedetermined pressure to estimate the unsprung weight of the axle 6, 10.

Figure 5 schematically illustrates a device 500. The control unit 120 and/orcomputer 130 described with reference to Figures 2 may in a version comprisethe device 500. The term "link" refers herein to a communication link whichmay be a physical connection such as an optoelectronic communication line,or a non-physical connection such as a wireless connection, e.g. a radio link ormicrowave link. The device 500 comprises a non-volatile memory 520, a dataprocessing unit 510 and a read/write memory 550. The non-volatile memory520 has a first memory element 530 in which a computer program, e.g. anoperating system, is stored for controlling the function of the device 500. Thedevice 500 further comprises a bus controller, a serial communication port, I/O means, an A/D converter, a time and date input and transfer unit, an event 28 counter and an interruption controller (not depicted). The non-volatile memory520 has also a second memory element 540.

There is provided a computer program Pr which comprises routines for amethod for load determination of a vehicle according to the invention. Thecomputer program Pr comprises routines for determining the load on asuspension means based on the pressure in the suspension means, theextension of the suspension means and the previous travel direction of thesuspension means. The computer program Pr comprises routines fordetermining the pressure in a suspension means. The computer program Prcomprises routines for determining the extension of a suspension means. Thecomputer program Pr comprises routines for determining the previous traveldirection of a suspension means. The computer program Pr comprisesroutines for determining the load on a suspension means base on apredetermined relationship between the pressure in a suspension means, theextension of a suspension means and the load on a suspension means,wherein the relationship depends on the previous travel direction of thesuspension means. The computer program Pr comprises routines fordetermining the vehicle pitch angle. The computer program Pr comprisesroutines for determining the road slope. The computer program Pr comprisesroutines for calibrating the relationship between the pressure in a suspensionmeans, the extension of a suspension means and the load on a suspensionmeans. The computer program Pr may be stored in an executable form or in acompressed form in a memory 560 and/or in a read/write memory 550.

Where the data processing unit 510 is described as performing a certainfunction, it means that the data processing unit 510 effects a certain part of theprogram stored in the memory 560 or a certain part of the program stored inthe read/write memory 550.

The data processing device 510 can communicate with a data port 599 via adata bus 515. The non-volatile memory 520 is intended for communication with 29 the data processing unit 510 via a data bus 512. The separate memory 560 isintended to communicate with the data processing unit 510 via a data bus 511.The read/write memory 550 is adapted to communicating with the dataprocessing unit 510 via a data bus 514.

When data are received on the data port 599, they are stored temporarily inthe second memory element 540. When input data received have beentemporarily stored, the data processing unit 510 is prepared to effect codeexecution as described above.

Parts of the methods herein described may be effected by the device 500 bymeans of the data processing unit 510 which runs the program stored in thememory 560 or the read/write memory 550. When the device 500 runs theprogram, methods herein described are executed.

The foregoing description of the preferred embodiments of the presentinvention is provided for illustrative and descriptive purposes. It is not intendedto be exhaustive or to restrict the invention to the variants described. Manymodifications and variations will obviously be apparent to one skilled in the art.The embodiments have been chosen and described in order best to explainthe principles of the invention and its practical applications and hence make itpossible for specialists to understand the invention for various embodiments and with the various modifications appropriate to the intended use.

Claims

1. A method for load determination of a vehicle (1 ), the vehicle (1) comprising achassis (3) and a pneumatic suspension system (200) with pneumaticsuspension means (201) arranged on at least one axle (6, 10), wherein theheight of the chassis (3) in relation to the at least one axle (6, 10) can bechanged by controlling the amount of air in the suspension means (201) andthereby changing the extension of the suspension means (201 ), characterizedby the step of, for each axle (6, 10): - determining (s100) the load on the suspension means (201) based on thepressure in the suspension means (201), the extension of the suspensionmeans (201), and the previous travel direction of the suspension means (201).

2. The method according to claim 1, wherein the method comprises the stepsof: - determining (s101) the pressure in the suspension means (201); - determining (s102) the extension of the suspension means (201); - determining (s103) the previous travel direction of the suspension means(201); and - determining (s104) the load on the suspension means (201) based on thedetermined data and a predetermined relationship between the load on thesuspension means (201), the pressure in the suspension means (201) and theextension of the suspension means (201), wherein the relationship depends onthe previous travel direction of the suspension means (201).

3. The method according to claim 2, wherein the load on the suspensionmeans (201) is determined (s104) based on a first three dimensional curve ofthe relationship between the load on the suspension means (201), thepressure in the suspension means (201) and the extension of the suspensionmeans (201) for a travel direction upwards or a second three dimensionalcurve of the relationship between the load on the suspension means (201), thepressure in the suspension means (201) and the extension of the suspensionmeans (201) for a travel direction downwards. 31

4. The method according to any of the preceding claims, wherein theextension of the suspension means (201) of an axle (6, 10) is determined by means of a chassis height sensor arranged in association with that axle (6, 10).

5. The method according to any of claims 1-3, wherein the extension of thesuspension means (201) of an axle (6, 10) is derived from the chassis heightat the other axles (6, 10) of the vehicle (1).

6. The method according to any of the preceding claims, wherein the load onthe suspension means (201) of each axle (6, 10) is further determined basedon the vehicle pitch angle.

7. The method according to any of the preceding claims, wherein the load onthe suspension means (201) of each axle (6, 10) is further determined basedon the road slope.

8. The method according to claims 6 and 7, wherein the vehicle pitch angleand the road slope are combined to a correction factor and multiplied with theload on the suspension means (201) determined based on the pressure in thesuspension means (201), the extension of the suspension means (201) andthe previous travel direction of the suspension means (201).

9. The method according to claim 6, wherein the vehicle pitch angle isdetermined based on the chassis height at the at least one front axle (6) andthe chassis height at the at least one rear axle (10).

10. The method according to any of the preceding claims, wherein the methodfurther comprises the steps of: - determining the unsprung weight associated with each axle (6, 10); and - determining the axle load for each axle by adding the unsprung weight to thedetermined load on the suspension means (201 ). 32

11. The method according to claim 10, wherein the unsprung weight is determined by measurement on a scale weighing machine.

12. A vehicle load sensing system (100) associated with a pneumaticsuspension system (200), the pneumatic suspension system (200) comprisingpneumatic suspension means (201) arranged on at least one axle (6, 10),wherein the height of a vehicle chassis (3) in relation to the at least one axle (6,10) can be changed by controlling the amount of air in the suspension means(201) and thereby changing the extension of the suspension means (201),characterized in that the vehicle load sensing system (100) comprises acontrol unit (120) adapted to determine the load on the suspension means(201) based on the pressure in the suspension means (201), the extension ofthe suspension means (201), and the previous travel direction of thesuspension means (201).

13. The system (100) according to claim 12, wherein the control unit (120) isadapted to determine the pressure in the suspension means (201); determinethe extension of the suspension means (201); determine the previous traveldirection of the suspension means (201); and to determine the load on thesuspension means (201) based on the determined data and a predeterminedrelationship between the load on the suspension means (201), the pressure inthe suspension means (201) and the extension of the suspension means (201 ),wherein the relationship depends on the previous travel direction of thesuspension means (201).

14. The system (100) according to claim 13, wherein the relationship betweenthe load on the suspension means (201), the pressure in the suspensionmeans (201) and the extension of the suspension means (201) for a traveldirection upwards is compiled in a first three dimensional curve in the controlunit (120) and a relationship between the load on the suspension means (102),the pressure in the suspension means (102) and the extension of the 33 suspension means (102) for a travel direction downwards is compiled in asecond three dimensional curve in the control unit (120).

15. The system (100) according to any of claims 12-14, wherein the controlunit (120) is adapted to determine the extension of the suspension means(201) of an axle (6, 10) by means of a chassis height sensor arranged inassociation with that axle (6, 10).

16. The system (100) according to any of claims 12-13, wherein the controlunit (120) is adapted to determine the extension of the suspension means(201) of an axle (6, 10) by calculation based on the chassis height at the otheraxles (6, 10) of the vehicle (1).

17. The system (100) according to any of claims 12-16, wherein the controlunit (120) is adapted to determine the load on the suspension means (201) ofeach axle (6, 10) based on the vehicle pitch angle.

18. The system (100) according to any of claims 12-17, wherein the controlunit (120) is adapted to determine the load on the suspension means (201) ofeach axle (6, 10) based on the road slope.

19. The system (100) according to claims 17 and 18, wherein the control unit(120) is adapted to combine the vehicle pitch angle and the road slope to acorrection factor and to multiply the correction factor with the load on thesuspension means (201) determined based on the pressure in the suspensionmeans (201), the extension of the suspension means (201) and the previoustravel direction of the suspension means (201 ).

20. The system (100) according to any of claims 12-19, wherein the controlunit (120) is adapted to determine the unsprung weight associated with eachaxle (6, 10); and to determine the axle load for each axle (6, 10) by adding theunsprung weight to the determined load on the suspension means (201). 34

21. A vehicle (1), comprising a vehicle load sensing system (100) according toany of claims 12-20,

22. A computer program (Pr), wherein said computer program comprisesprogram code for causing an electronic control unit (120; 500) or a computer(130; 500) connected to the electronic control unit (120; 500) to perform thesteps according to any of the claims 1-1 1.

23. A computer program product comprising a program code stored on acomputer-readable medium for performing the method steps according to anyof claims 1-11, when said computer program is run on an electronic control unit(120; 500) or a computer (130; 500) connected to the electronic control unit(120; 500).