SE1951335A1

SE1951335A1 - A method for detecting leakage in a hydraulic steering system, a control device, a vehicle, a computer program and a computer-readable medium

Info

Publication number: SE1951335A1
Application number: SE1951335A
Authority: SE
Inventors: Lars Soldagg
Original assignee: Scania Cv Ab
Priority date: 2019-11-22
Filing date: 2019-11-22
Publication date: 2021-05-23
Also published as: DE102020127296A1; SE543750C2; DE102020127296B4

Abstract

The present invention relates to a method for detecting leakage in a hydraulic steering system (10), the hydraulic steering system (10) comprising: a hydraulic cylinder (20) with a piston (22) movably arranged inside the cylinder (20) forming a first chamber (24) and a second chamber (26); and a position sensor (30) arranged to determine the position of the piston (22), wherein the piston (22) is connected to wheels (6) of a wheel axle (8), such that movement of the piston (22) will steer the wheels (6), the method comprising: steering (s101) the wheels (6) from a centre position (Pc) to a first predetermined position (P1) by controlling the piston (22) in a first direction (D1); and detecting (s102) leakage in the hydraulic steering system (10) based on a detected movement of the piston (22) in a second direction (D2), opposite to the first direction (D1), wherein any movement of the piston (22) is detected by means of the position sensor (30).

Description

A method for detecting Ieakage in a hydraulic steering system, a controldevice, a vehicle, a computer program and a computer-readable medium TECHNICAL FIELD The invention relates to a method for detecting Ieakage in a hydraulic steeringsystem of a vehicle. The invention also relates to a control device for detectingIeakage in a hydraulic steering system, a vehicle comprising such a control device, a computer program and a computer-readable medium.

BACKGROUND Vehicles today may comprise hydraulic steering systems for steering thewheels of the vehicle. Such system typically comprises a hydraulic cylinderwith a reciprocating piston applying a force to steer the wheels. The piston isconnected to the wheels, such that moving the piston turns the wheels. Valvesmay be controlled to regulate the flow of working liquid/hydraulic fluid to thehydraulic cylinder, based on the torque applied on the steering wheel of thevehicle. A hydraulic steering system may also comprise a position sensor fordetermining the position of the piston in the cylinder and thus monitoring thesteering angle. For example, wheel axles may be locked in a position wherethe wheels point straight ahead when the vehicle is operating at high speed.This means that the piston should be kept in a centre position. lf the pistonmoves out of its centre position during such operation, it can be assumed thateither there is a Ieakage in the system, or the system has been subjected tohigh impulse forces induced from the road. Thus, unexpected movement ofthe piston may indicate Ieakage or potentially reckless driving behaviour. lntoday's systems, the vehicle operator may be informed about the unexpectedmovement and/or the operator may be prompted to go to a workshop toinvestigate the assumed Ieakage. ln a hydraulic steering system, there may be several different reasons for aIeakage and the fact that the piston moves does not explain where the Ieakageis originated. The reason for the Ieakage will thus have to be investigated atthe workshop and this may be a time consuming procedure. The vehicle maythus spend a lot of time at the workshop, which is disadvantageous.

SUMMARY Despite known solutions in the field, it would be desirable to develop a methodfor detecting Ieakage in a hydraulic steering system of a vehicle, whichalleviates or at least reduces drawbacks with prior art.

The object of the present invention is therefore to achieve a new andadvantageous method, which enables detection and verification of smallinternal leakages in a hydraulic steering system of a vehicle. Another object isto achieve a new and advantageous method for detecting Ieakage in ahydraulic steering system of a vehicle, which method results in a precisejudgment of the faulty component causing the Ieakage and thereby enables aquicker and more correct repair of the hydraulic steering system.

The herein mentioned objects are achieved by a method for detecting Ieakagein a hydraulic steering system, a control device for detecting Ieakage in ahydraulic steering system, a vehicle, a computer program and a computer-readable medium according to the independent claims.

Hence, according to an aspect of the present invention, a method for detectingIeakage in a hydraulic steering system of a vehicle is provided, the hydraulicsteering system comprising: a hydraulic cylinder with a piston movablyarranged inside the cylinder forming a first chamber and a second chamberinside the cylinder; and a position sensor arranged to determine the position of the piston inside the cylinder, wherein the piston is connected to wheels of a wheel axle, such that movement of the piston will steer the wheels. Themethod comprises: steering the wheels from a centre position to a firstpredetermined position by controlling the piston in a first direction; anddetecting Ieakage in the hydraulic steering system based on a detectedmovement of the piston in a second direction, opposite to the first direction,wherein any movement of the piston is detected by means of the position SenSOF.

According to another aspect of the invention, a control device for detectingIeakage in a hydraulic steering system of a vehicle is provided, the hydraulicsteering system comprising: a hydraulic cylinder with a piston movablyarranged inside the cylinder forming a first chamber and a second chamberinside the cylinder; and a position sensor arranged to determine the positionof the piston inside the cylinder, wherein the piston is connected to wheels ofa wheel axle, such that movement of the piston will steer the wheels, whereinthe control device is arranged in communication with the position sensor andis configured to, after the wheels have been steered from a centre position toa first predetermined position by controlling the piston in a first direction, detectIeakage in the hydraulic steering system based on a detected movement ofthe piston in a second direction, opposite to the first direction, wherein anymovement of the piston is detected by means of the position sensor.

According to yet another aspect of the invention, a vehicle with a hydraulicsteering system is provided, the hydraulic steering system comprising: ahydraulic cylinder with a piston movably arranged inside the cylinder forminga first chamber and a second chamber inside the cylinder; and a positionsensor arranged to determine the position of the piston inside the cylinder,wherein the piston is connected to wheels of a wheel axle of the vehicle, suchthat movement of the piston will steer the wheels, wherein the vehicle furthercomprises a control device as disclosed herein.

A hydraulic steering system for a vehicle comprises a plurality of components,which for various reasons may malfunction and/or cause a Ieakage. ExternalIeakage may be visually easy to detect but Ieakage internally of the hydraulicsteering system may be very difficult to detect and it may be very difficult toidentify which component causes the Ieakage. lnternal Ieakage may forexample be caused by fau|ty pressure valves typically arranged on each sideof the piston, or a fau|ty piston sea|. Today, it is known to detect unexpectedmovement of the piston in a hydraulic steering system and thereby identify apossible Ieakage. To determine where the Ieakage is, tests must be performedin a workshop or the whole arrangement with cylinder, piston and valves mayhave to be exchanged to ensure that the Ieakage is removed. This is verycostly. Steering the wheels from a centre position to a first predeterminedposition according to the present invention, means that the piston is controlledto be displaced in a first direction. The first chamber of the cylinder is formedon one side of the piston and the second chamber of the cylinder is formed onthe other side of the piston. Thus, by controlling the piston in the first direction,one of the first chamber and the second chamber becomes smaller and theother chamber becomes larger. Specifically, the chamber on the side of thepiston in which direction the piston is controlled to be displaced, will be smaller.The first chamber may be on a first side of the piston and the second chamberis on the second side of the piston. Thus, controlling the piston in a firstdirection may decrease the volume of the first chamber and increase thevolume of the second chamber, and vice versa. After having steered thewheels to the first predetermined position, due to the elastic hysteresis of thetyres of the wheels, a force directed to turn the wheels back towards the centreposition will be created and a force in the second direction will thereby beapplied on the piston. The pressure inside the second chamber, whichpreviously was actively enlarged by controlling the piston in the first direction,will thereby increase. lf there is no Ieakage, the piston will remain in the sameposition despite the applied force. When there is a Ieakage in association withthe second chamber or in the piston seal, the force on the piston caused by the tyre hysteresis will cause the hydraulic fluid to move out of the second Chamber, to the exterior in the event of external Ieakage, or to the first chamberin the event of internal Ieakage, to reduce the pressure in the second chamber.The piston will thereby move in the second direction. Any detected movementof the piston in the second direction is thus a reactive movement, caused bythe tyre hysteresis. Thus, by steering the wheels and the piston in a firstdirection and subsequently detect movement of the piston in the seconddirection, opposite to the first direction, it can be conc|uded that there may bea Ieakage in association with the second chamber or in the piston seal. Thisway, not only is Ieakage detected but the faulty component is also identified orthe cause of the Ieakage is at least narrowed down, for example to the accurateside of the piston. The workshop may this way spend less time on identifyingthe faulty component and can make a quick and correct repair. The vehicle willspend less time at the workshop, which will reduce the cost for the vehicleowner and only the faulty component may be replaced instead of the wholecylinder arrangement. Furthermore, by using the natural phenomena ofhysteresis in the wheel tyres, the method does not have to involve activecontrol or externally applied loads/forces on the piston to detect Ieakage in thehydraulic steering system. The method according to the present disclosure is thereby less complex, less expensive and more efficient.

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 examples of the invention aredescribed below, 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.

BRIEF DESCRIPTION OF THE DRAWINGS For better 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 notations denote similar items in the various diagrams, and in which: Figure 1 schematically illustrates a side view of a vehicle according to anexample; Figure 2 schematically illustrates details of a hydraulic steering system fora vehicle according to an example; Figure 3 schematically illustrates a block diagram of a method fordetecting leakage in a hydraulic steering system according to anexample; Figure 4a-b schematically illustrate details of a vehicle during a method fordetecting leakage in a hydraulic steering system according to anexample Figure 5 illustrates graphs relating to a method for detecting leakage in ahydraulic steering system according to an example; and Figure 6 schematically illustrates a control device or computer according to an example.

DETAILED DESCRIPTION To improve the handling of leakage in a hydraulic steering system, a method,a control device and a vehicle according to the disclosure has been developed.

Hence, according to an aspect of the present disclosure, a method fordetecting leakage in a hydraulic steering system is provided, the hydraulicsteering system comprising: a hydraulic cylinder with a piston movablyarranged inside the cylinder forming a first chamber and a second chamber inside the cylinder; and a position sensor arranged to determine the positionof the piston inside the cylinder, wherein the piston is connected to wheels ofa wheel axle, such that movement of the piston will steer the wheels. Themethod comprises: steering the wheels from a centre position to a firstpredetermined position by controlling the piston in a first direction; anddetecting Ieakage in the hydraulic steering system based on a detectedmovement of the piston in a second direction, opposite to the first direction,wherein any movement of the piston is detected by means of the positionsensor. As previously described, any detected movement of the piston in thesecond direction is caused by tyre hysteresis. The detected movement of thepiston in the second direction is thus a reactive movement or non-controlled movement. lt is to be understood that the exact configuration of the hydraulic steeringsystem and how the piston is connected to the wheel axle is not part of theinvention per se. The hydraulic steering system may thus be configured asconventional hydraulic steering systems.

The hydraulic cylinder may be a double-acting cylinder. The hydraulic cylinderaccommodates a hydraulic fluid. The first chamber of the cylinder may beformed on a first side of the piston and the second chamber may be formed ona second side of the piston. Detected movement of the piston in the seconddirection may indicate Ieakage in association with the second chamber. Thismay also be referred to as Ieakage on the second side of the piston. Thehydraulic steering system may comprise a piston seal arranged to sealbetween the piston and the cylinder and thereby ensure that hydraulic fluidcannot flow past the piston between the chambers. Displacing the piston in thefirst direction may decrease the volume of the first chamber and increase thevolume of the second chamber, and vice versa. The first chamber and thesecond chamber may be arranged in fluid communication with a receptacle forthe hydraulic fluid. To steer the wheels, the hydraulic steering system is controlled, so that hydraulic fluid is flowing from one chamber to the other, whereby the pressure will increase in the chamber receiving the hydraulic fluid.The piston will thereby be displaced, so that the receiving chamber isincreasing in volume and the pressure is decreased. Since the piston isconnected to the wheels, the wheels will be turned when the piston isdisplaced. Thus, steering the wheels by controlling the piston in a first directioncomprises controlling the flow of hydraulic fluid in the hydraulic steeringsystem, so that the piston is displaced in the first direction. As an example, tosteer the wheels in a first steer direction, the hydraulic steering system may becontrolled so that hydraulic fluid in the first chamber will flow to the secondchamber. The amount of hydraulic fluid in the second chamber is therebyincreased and the piston is thereby controlled to be displaced in the firstdirection. Similarly, to steer the wheels in a second steer direction, thehydraulic steering system is controlled so that hydraulic fluid in the secondchamber will flow to the first chamber, such that the amount of hydraulic fluidin the first chamber is increased and the piston is thereby controlled to bedisplaced in the second direction. The hydraulic fluid may flow between thechambers via the receptacle.

The hydraulic steering system may further comprise a hydraulic pump. Thehydraulic fluid may be circulated in the hydraulic steering system by means ofthe hydraulic pump. Thus, intended and controlled displacement of the pistonis achieved by means of a hydraulic pump, whereas the detected movementcaused by hysteresis of the wheels is a movement achieved without theinfluence of the hydraulic pump. Steering the wheels from a centre position toa first predetermined position by controlling the piston in a first direction maythus comprise controlling the hydraulic pump, so that the piston is displaced inthe first direction. The flow of hydraulic fluid into the respective chamber mayfurther be regulated by controlling a valve arrangement. The hydraulic steeringsystem may thus comprise a valve arrangement.

The piston may have a centre position, corresponding to the centre position of the wheels. The centre position of the wheels means that the wheels are pointing straight ahead. The centre position of the piston may be a positionwhere the first chamber and the second chamber are essentially equal involume. The piston may be directly or indirectly connected to the wheels, aslong as displacement of the piston in the first or second direction can turn the wheels.

The position sensor may be arranged in association with the piston in thecylinder. The position sensor may thus be referred to as a cylinder pistonsensor. The position sensor may be a sensor with relatively high precision inorder to enable detecting small movements of the piston. As an example, theposition sensor may be configured to detect piston movements of 0,1millimetres or more. The precision and accuracy of the position sensor may beadapted to the size of leakage that is desired to detect. Thus, the smallermovements the position sensor is configured to detect, the smaller leakagescan be detected. The position sensor may be a linear sensor. For example,the position sensor may be a linear transducer. lt is to be understood that theposition sensor may be any sensor arranged anywhere in the hydraulicsteering system to indirectly or directly detect piston movements.

According to an example, the method further comprises steering the wheels toa second predetermined position by controlling the piston in the seconddirection; and detecting leakage in the hydraulic steering system based on adetected movement of the piston in the first direction. Detecting movement ofthe piston in the first direction may indicate leakage in association with the firstchamber. This may also be referred to as leakage on the first side of the piston.As previously discussed, by controlling the piston in a first direction andsubsequently detect movement of the piston in the second direction, oppositeto the first direction, it can be concluded that there may be a leakage inassociation with the second chamber or in the piston seal. The detectedmovement of the piston in the first direction after having controlled the pistonin the second direction, is a reactive or non-controlled movement caused by tyre hysteresis. To be able to determine if there is a leakage also in the other Chamber, it may be required to perform the method in both directions. Steeringthe wheels to the second predetermined position thus comprises steering thewheels in an opposite direction to when the wheels were steered to the firstpredetermined position. Thus, the wheels may be steered from the centreposition to the first predetermined position, and tyre hysteresis will then createa force directed to turn the wheels back towards the centre position. A forcedirected in the second direction, opposite to the first direction, will thereby beapplied on the piston. lf there is a Ieakage, the hydraulic f|uid will flow from thesecond chamber to the first chamber and the piston will move in the seconddirection. The piston movement will be detected by the piston sensor and aIeakage in the second chamber or in the piston sea| can be concluded. Thewheels are subsequently steered to a second predetermined position bycontrolling the piston in the second direction. Tyre hysteresis will then createa force directed to turn the wheels back to the first predetermined position. Aforce directed in the first direction will thereby be applied on the piston and ifthere is a Ieakage, the hydraulic f|uid will flow from the first chamber to thesecond chamber and the piston will move in the first direction. The pistonmovement will be detected by the piston sensor and a Ieakage in the firstchamber or in the piston sea| can be concluded. This way, Ieakage on bothsides of the piston can be detected in a time efficient and simple way.

The first predetermined position of the wheels may be a position halfvvay to themaximally turned position of the wheels. The first predetermined position mayhave been empirically determined to a position where the force created by thetyre hysteresis is as large as possible. The second predetermined position ofthe wheels may be the centre position of the wheels. The wheels may thus firstbe turned halfvvay to detect Ieakage in one of the chambers, and subsequentlybe turned back to the centre position to detect Ieakage in the other chamber.Alternatively, the second predetermined position is a position halfvvay to themaximally turned position of the wheels, in the opposite direction to the firstpredetermined position. The first predetermined position may thus be a turned position to the right and the second predetermined position may be a turned 11 position to the left, or vice versa. ln this case, the step of steering the wheelsto the second predetermined position may comprise steering the wheels fromthe centre position to the second predetermined position. The wheels may thushave been steered to the centre position after having detected Ieakage in oneof the chambers, before being turned to detect Ieakage in the other chamber.

The step of steering the wheels may be performed manually or automatically.The step of steering the wheels may thus be performed by manuallymanoeuvring a steering wheel of the vehicle, whereby the piston is controlledto be displaced and thereby turn the wheels. Alternatively, the wheels aresteered automatically by automatically controlling the steering column andthereby control the piston.

According to an example, movement of the piston in the first direction indicatesIeakage in a first valve arranged in association with the first chamber of thecylinder. That is, non-controlled movement of the piston in the first directionmay indicate Ieakage in a first valve arranged in association with the firstchamber of the cylinder. lf the first valve is leaking, the increased pressure inthe first chamber, caused by the force acting on the piston in the first direction,will result in hydraulic fluid leaking out from the first chamber via the faulty firstvalve. The hydraulic fluid leaking from the first chamber may flow back to areceptacle for the hydraulic fluid. Similarly, non-controlled movement of thepiston in the second direction may indicate Ieakage in a second valve arrangedin association with the second chamber of the cylinder. The valve arrangementof the hydraulic steering system may thus comprise a first valve arranged inassociation with the first chamber and a second valve arranged in associationwith the second chamber. The first valve and the second valve may becontrollable to regulate the flow of hydraulic fluid into the first chamber and thesecond chamber respectively. The first valve and the second valve may bepressure relief valves allowing flow of hydraulic fluid in one direction to reducethe pressure in the chambers. Alternatively, the first valve and the second valve are pressure relief valves configured to allow flow only in one direction. 12 According to an example, Ieakage may be detected when the detected pistonmovement exceeds a predetermined threshold distance. Thus, some minormovement of the piston caused by the tyre hysteresis may be acceptable andmay not indicate a Ieakage. The predetermined threshold distance may bewithin the range of 0,2-0,5 millimetres. This means that when the positionsensor detects a movement of the piston that exceeds for example 0,2mi||imetres, it is concluded that there is a Ieakage. ln the event that the pistonis not moving, or is moving less than the predetermined threshold distance, itis concluded that there is no Ieakage in the hydraulic steering system. As anexample, an unexpected movement of the piston may have been detectedduring operation of the vehicle, and the method according to the presentdisclosure is subsequently performed at a workshop to verify the Ieakageand/or identify the faulty component. lf the result of the method is that noIeakage is detected, the previously detected movement of the piston may havebeen caused by high impulse forces induced from the road on the wheels,which causes the first and/or second valve to open and thereby enable movement of the piston.

The method may comprise providing an alert when Ieakage is detected. Thealert may be an audial, visual or tactile alert. Additionally or alternatively, themethod comprises providing instructions to take the vehicle to a workshop.Such instructions may be provided on a display in the vehicle or a display in acontrol centre in the event that the vehicle is an autonomously operatedvehicle.

According to an example, the method according to the disclosure is performedat a workshop. Vehicles today may already comprise a function to detect apotential Ieakage in the hydraulic steering system. There may, however, stillbe a need to determine the cause of the Ieakage, and thus where the Ieakageis situated. The operator of the vehicle may thus receive an alert or be prompted to take the vehicle to a workshop where the method according to 13 this disclosure may be performed. The method may thus be performed as atrouble shooting process to identify the cause of the leakage, when the vehiclealready has concluded that there might be a leakage. The method may beinitiated manually. As an example, the service technician may connect with acontrol unit of the vehicle and initiate the method. ln the event that the methodis performed at a workshop, the method may further comprise displayinginformation about where in the hydraulic steering system the leakage issituated. As an example, the method may comprise displaying an image of thehydraulic steering system to visualise where the leakage is situated. This way,the service technician can easily determine where to start looking for the leakage and quickly resolve the problem.

According to another example, the method according to the disclosure isautomatically performed. The method may for example be performed duringstart-up of the vehicle. ln this case, the method may comprise providing analert if a leakage is detected. Alternatively, the method may comprise providinginstructions to take the vehicle to a workshop as soon as possible. Such alertand/or instructions may be configured so that it cannot be removed by thevehicle operator but requires a service technician to be removed. The vehiclewill thus have to be operated to a workshop to investigate the problem and getthe instructions removed. The information provided to the vehicle operator maydepend on the magnitude of the detected leakage. Typically, if the detectedleakage is relatively small, an alert may be provided and if the detectedleakage is relatively large, the operator may be instructed to go to a workshopimmediately. When the control device has detected a leakage, the controldevice may be configured to save this in a memory of the control device. Whena service technician connects with the control device, the service technicianwill this way be able to receive information about the detected leakage andwhere the leakage is situated.

Detecting leakage in the hydraulic steering system based on the detected movement of the piston may also comprise determining the size of the leakage 14 based on the speed of the piston movement. The larger the leakage, the fastermoves the piston. The speed of the piston movement may bedetermined/calculated by determining the movement of the piston over time.The piston movement may for example be measured for a predeterminedperiod of time, and the piston speed may be calculated based on themovement during this predetermined period oftime. The predetermined periodof time may be referred to as a detecting time. The piston movement may bedefined as the distance the piston has moved from a piston positioncorresponding to the first predetermined position of the wheels or the secondpredetermined position of the wheels. The predetermined period of time mayvary depending on the configuration of the hydraulic steering system and thecurrent application. The predetermined period of time may also depend on theaccuracy of the position sensor and how small leakages that are interesting todetect. Typically, the piston will move from the very second the wheel has beensteered to the predetermined position until the hydraulic fluid has leaked somuch that the pressure caused by the hysteresis force is negligible. Smallleakages will thus require more detecting time than large leakages. Generally,the piston will move faster in the beginning when the wheels have been steeredand the hysteresis force starts acting on the piston. This is because thepressure in the chamber associated with the leakage is larger at the beginning,before the hydraulic fluid has leaked out. Thus, in order to determine the sizeof the leakage it may be suitable to select a detecting time between 15-30seconds. As an example, a piston speed below a speed threshold value maybe considered a small leakage and a piston speed above the speed thresholdvalue may be considered a large leakage. Alternatively, the control device maycomprise a look-up table or list of predetermined piston speeds andcorresponding leakage sizes saved in a database, wherein determining thesize of the leakage comprises comparing the determined piston speed with thelist. The leakage size may thus be determined by means of data mapping.

Detected non-controlled movement of the piston in the first direction and the second direction may indicate leakage in both the first valve and the second valve, or Ieakage in the piston seal between the first and second Chamber.Typically, if the size of the Ieakage is equal in both directions, that is, if the sizeof the Ieakage is equal on both sides of the piston, it may indicate that the Ieakage is in the piston seal.

According to another aspect of the present disclosure, a control device fordetecting Ieakage in a hydraulic steering system of a vehicle is provided. Thehydraulic steering system comprises: a hydraulic cylinder with a pistonmovably arranged inside the cylinder forming a first chamber and a secondchamber inside the cylinder; and a position sensor arranged to determine theposition of the piston inside the cylinder, wherein the piston is connected towheels of a wheel axle, such that movement of the piston will steer the wheels,wherein the control device is arranged in communication with the positionsensor and is configured to, after the wheels have been steered from a centreposition to a first predetermined position by controlling the piston in a firstdirection, detect Ieakage in the hydraulic steering system based on a detectedmovement of the piston in a second direction, opposite to the first direction,wherein any movement of the piston is detected by means of the position SenSOF. lt will be appreciated that all the embodiments described for the control deviceaspect of the disclosure are also applicable to the method aspect of thedisclosure, and vice versa. The control device may be implemented as aseparate entity or distributed in two or more physical entities. The controldevice may comprise one or more control units and/or computers. The controldevice may thus be implemented or realised by the control device comprisinga processor and a memory, the memory comprising instructions, which whenexecuted by the processor causes the control device to perform the hereindisclosed method. The control device may be comprised in the hydraulic steering system, or the control device may be a vehicle external control device. 16 The control device may be configured to, after the wheels have been steeredto a second predetermined position by controlling the piston in the seconddirection, detect Ieakage in the hydraulic steering system based on a detectedmovement of the piston in the first direction. The control device may beconfigured to detect a Ieakage when the detected piston movement exceedsa predetermined threshold distance. The control device may be configured todetect a predetermined threshold distance within the range of 0,2-0,5 millimetres.

Ieakage when the detected piston movement exceeds a The control device may be configured to determine the size of the Ieakagebased on the speed of the piston movement. The control device may beconfigured to determine the speed of the piston movement, also called pistonspeed. The control device may be configured to steer the wheels from thecentre position to the first predetermined position by controlling the piston inthe first direction. The control device may also be configured to steer thewheels to the second predetermined position by controlling the piston in thesecond direction. The control device is typically configured to steer the wheelswhen the method according to the disclosure is performed automatically, forexample during start-up of the vehicle. Alternatively, the control device isconfigured to display instructions to a vehicle operator or service technician tomanually steering the wheels.

According to yet another aspect of the present disclosure, a vehicle with ahydraulic steering system is provided. The hydraulic steering systemcomprises: a hydraulic cylinder with a piston movably arranged inside thecylinderforming a first chamber and a second chamber inside the cylinder; anda position sensor arranged to determine the position of the piston inside thecylinder, wherein the piston is connected to wheels of a wheel axle of thevehicle, such that movement of the piston will steer the wheels. The vehiclefurther comprises a control device as disclosed herein. The control device maythus be part of the vehicle and the method may be performed automatically by 17 means of the control device. Alternatively, the control device is situated in aworkshop and is connected to the vehicle to perform the method.

The present disclosure will now be further i||ustrated with reference to the appended figures.

Figure 1 schematically i||ustrates a side view of a vehicle 1 according to anexample. The exemplified vehicle 1 may be a heavy vehicle in the shape of atruck, bus or similar. The vehicle 1 may comprise a propulsion unit 2, a gearbox4, and a hydraulic steering system 10 for steering the wheels 6 of a wheel axle8. The hydraulic steering system 10 will be further described with regard toFigure 2, 3, 4a-b and 5. The propulsion unit 2 may comprise an internalcombustion engine or an electrical machine. The wheels 6 steered by meansof the hydraulic steering system 10 comprise tyres 12.

Figure 2 schematically i||ustrates details of a hydraulic steering system 10 fora vehicle 1 according to an example. The vehicle 1 may be configured asdisclosed in Figure 1. Figure 2 i||ustrates a wheel axle 8 with the wheels 6 in acentre position Pc and thus being arranged in parallel and pointing straightahead. The hydraulic steering system 10 comprises a hydraulic cylinder 20with a piston 22 movably arranged inside the cylinder 20 forming a firstchamber 24 and a second chamber 26 inside the cylinder 20; and a positionsensor 30 arranged to determine the position of the piston 22 inside thecylinder 20. The piston 22 is connected to the wheels 6 of the wheel axle 8,such that movement of the piston 22 will steer the wheels 6.

The hydraulic cylinder 20 may be a double-acting cylinder. The hydrauliccylinder 20 accommodates a hydraulic fluid 28. The first chamber of thecylinder 24 may be formed on a first side of the piston 22 and the secondchamber 26 may be formed on a second side of the piston 22. The hydraulicsteering system may comprise a piston seal 23 arranged to seal between the piston 22 and the cylinder 20 and thereby ensure that hydraulic fluid 28 cannot 18 flow past the piston 22 between the chambers 24, 26. The hydraulic steeringsystem 10 may further comprise a receptacle 40 for hydraulic fluid 28. The firstchamber 24 and the second chamber 26 may be arranged in fluidcommunication with this receptacle 40.

The hydraulic steering system 10 may further comprise a hydraulic pump 42.The hydraulic fluid 28 may be circulated in the hydraulic steering system 10 bymeans of the hydraulic pump 42. The hydraulic steering system 10 may alsocomprise a valve arrangement 50 for regulating the flow of hydraulic fluid 28into the chambers 24, 26. The valve arrangement 50 may comprise a first valve52 and a second valve 54. The first valve 52 may be arranged in associationwith the first chamber 24 and the second valve 54 may be arranged inassociation with the second chamber 26.

The position sensor 30 may be arranged in association with the piston 22 inthe cylinder 20. The position sensor 30 may be a sensor with relatively highprecision in order to enable detecting small movements of the piston 22. Theposition sensor 30 may be a linear sensor.

The hydraulic steering system 10 may further comprise a control device 100.The control device 100 may be configured to detect leakage in the hydraulicsteering system 10. The control device 100 may be arranged in communicationwith the position sensor 30, the valves 52, 54, and the hydraulic pump 42. Thecontrol device 100 is configured to, after the wheels 6 have been steered froma centre position Pc to a first predetermined position P1 (see Figure 4a) bycontrolling the piston 22 in a first direction D1, detect leakage in the hydraulicsteering system 10 based on a detected self-movement or non-controlledmovement of the piston 22 in a second direction D2, opposite to the firstdirection D1, wherein any movement of the piston 22 is detected by means ofthe position sensor 30. The control device 100 may also be configured to steerthe wheels 6 from the centre position Pc to the first predetermined position P1 by controlling the piston 22 in a first direction D1. The control device 100 may 19 be configured to control the hydraulic pump 42 and/or the valves 52, 54, suchthat the piston 22 is displaced in the first direction D1, in order to steer the wheels 6 from the centre position Pc to the first predetermined position P1.

The control device 100 may be configured to, after the wheels 6 have beensteered to a second predetermined position P2 (see Figure 4b) by controllingthe piston 22 in the second direction D2, detect Ieakage in the hydraulicsteering system 10 based on a detected movement of the piston 22 in the firstdirection D1. The control device 100 may also be configured to steer thewheels 6 to the second predetermined position P2 by controlling the piston 22in the second direction D2. The control device 100 may be configured to controlthe hydraulic pump 42 and/or the valves 52, 54, such that the piston 22 isdisplaced in the second direction D2, in order to steer the wheels 6 to thesecond predetermined position P2.

The control device 100 may further be configured to detect a Ieakage whenthe detected piston movement exceeds a predetermined threshold distance.The control device 100 may be configured to detect a Ieakage when thedetected piston movement exceeds a predetermined threshold distance withinthe range of 0,2-0,5 millimetres. Also, the control device 100 may beconfigured to determine the size of the Ieakage based on the speed of thepiston movement. The control device 100 may be configured to determine thespeed of the piston movement, also called piston speed, based on the changeof piston position over time. The control device 100 may be configured todisplay instructions to a vehicle operator or service technician to manuallysteer the wheels 6 to the first predetermined position P1 or the secondpredetermined position P2. The control device 100 may further be configuredto display an image of the hydraulic steering system indicating where theIeakage is situated.

Fig. 3 schematically illustrates a block diagram of a method for detecting Ieakage in hydraulic steering system 10 of a vehicle 1. The method may relate to a vehicle 1 as disclosed in Figure 1 and a hydraulic steering system 10 asdisclosed in Figure 2. The method may be performed by a control device 100as disclosed in Figure 2 or Figure 6. Figures 4a and 4b schematically illustratesexamples of a vehicle performing the method. The method will thus bedescribed with regard to both Figure 3 and Figures 4a and 4b. ln figures 4aand 4b, only the components associated with the cylinder 20 of the hydraulicsteering system 10 is shown for clarity. The method comprises: steering s101the wheels 6 from a centre position Pc to a first predetermined position P1 bycontrolling the piston 22 in a first direction D1; and detecting leakage in thehydraulic steering system 10 based on a detected movement of the piston 22in a second direction D2, opposite to the first direction D1, wherein anymovement of the piston 22 is detected by means of the position sensor 30.

Figure 4a shows the vehicle 1 when the wheels 6 have been steered to thefirst predetermined position P1 by controlling the piston 22 in the first directionD1.The turning force acting on the wheels 6 when steering them to the firstpredetermined position P1 is illustrated with a dotted arrow. By controlling thepiston 22 in the first direction D1, the first chamber 24 becomes smaller andthe second chamber 26 becomes larger. After having steered the wheels 6 tothe first predetermined position P1, a turning force TF2 directed to turn thewheels 6 back towards the centre position Pc will be created due to the elastichysteresis of the tyres 12 of the wheels 6. This turning force TF2 is illustratedwith an arrow in the figure. A force F2 in the second direction D2 will therebybe applied on the piston 22. The pressure inside the second chamber 26 willthereby increase. lf there is no leakage, the piston 22 will remain in the sameposition despite the applied force F2. When there is a leakage in associationwith the second chamber 26 or the piston seal 23, the force F2 on the piston22 caused by the tyre hysteresis will cause the hydraulic fluid 28 to move outof the second chamber 26 to the first chamber 24, to reduce the pressure inthe second chamber 26. The piston 22 will thereby move in the seconddirection D2. Thus, movement of the piston 22 in the second direction D2 21 indicates a Ieakage in association with the second Chamber 26 or the pistonsea|23.

Steering s101 the wheels 6 from the centre position Pc to the firstpredetermined position P1 by controlling the piston 22 in the first direction D1may comprise controlling the flow of hydraulic fluid 28 in the hydraulic steeringsystem 10, so that the piston 22 is displaced in the first direction D1. Steerings101 the wheels 6 from the centre position Pc to the first predeterminedposition P1 by controlling the piston 22 in the first direction D1 may comprisecontrolling the hydraulic pump 42, so that the piston 22 is displaced in the firstdirection D1. The flow of hydraulic fluid 28 into the respective chamber 24, 26may further be regulated by controlling the valve arrangement 50.

The method may further comprise steering s103 the wheels 6 to a secondpredetermined position P2 by controlling the piston 22 in the second directionD2; and detecting s104 Ieakage in the hydraulic steering system 10 based ona detected movement of the piston 22 in the first direction D1. Figure 4b showsa situation where the wheels 6 have been steered to the second predeterminedposition P2. The turning force acting on the wheels 6 when steering them tothe second predetermined position P2 is illustrated with a dotted arrow. ln thisexample, the second predetermined position P2 is the centre position Pc. Afterhaving steered the wheels 6 to the second predetermined position P2, aturning force TF1 directed to turn the wheels 6 back towards the firstpredetermined position P1 will be created due to the elastic hysteresis of thetyres 12 of the wheels 6. This turning force TF1 is illustrated with an arrow inthe figure. A force F1 in the first direction D1 will thereby be applied on thepiston 22. The pressure inside the first chamber 24 will thereby increase. lfthere is no Ieakage, the piston 22 will remain in the same position despite theapplied force F1. When there is a Ieakage in association with the first chamber24 or the piston seal 23, the force F1 on the piston 22 caused by the tyrehysteresis will cause the hydraulic ﬂuid 28 to move out of the first chamber 24 into the second chamber 26, to reduce the pressure in the first chamber 24. 22 The piston 22 will thereby move in the first direction D1. Thus, movement ofthe piston 22 in the first direction D1 indicates a Ieakage in association withthe first chamber 24 or the piston seal 23. By these additional method steps,Ieakage on both sides of the piston 22 can be detected in a time efficient and simple way.

The step of steering s101, s103 the wheels 6 may be performed manually orautomatically. Detecting s102 Ieakage in the hydraulic steering system 10based on a detected movement of the piston 22 in a second direction D2 mayindicate Ieakage in the second valve 54. Detecting s104 Ieakage in thehydraulic steering system 10 based on a detected movement of the piston 22in the first direction D1 may indicate Ieakage in the first valve 52.

Leakage may be detected s102, s104 when the detected piston movementexceeds a predetermined threshold distance. Thus, minor movement of thepiston 22 caused by the tyre hysteresis may not indicate a Ieakage. Thepredetermined threshold distance may be within the range of 0,2-0,5 millimetres.

The method may optionally comprise providing an alert when Ieakage isdetected. The alert may be an audial, visual or tactile alert. Additionally oralternatively, the method comprises providing instructions to take the vehicle1 to a workshop. Such instructions may be provided on a display in the vehicle1 or a display in a control centre in the event that the vehicle 1 is anautonomously operated vehicle.

The method may be performed at a workshop for trouble shooting. The methodmay be initiated manually, for example by manoeuvring a steering wheel of thevehicle 1 to steer s101, s103 the wheels 6. The method may further comprisedisplaying information about where in the hydraulic steering system 10 theIeakage is situated. As an example, the method may comprise displaying an image of the hydraulic steering system 10 to visualise where the Ieakage is 23 situated. This way, the service technician can easily determine where to startlooking for the leakage and quickly resolve the problem.

The method may be automatically performed. The method may for examplebe performed during start-up of the vehicle 1. ln this case, the method maycomprise providing an alert if a leakage is detected. Alternatively, the methodmay comprise providing instructions to take the vehicle 1 to a workshop assoon as possible. lf the detected leakage is relatively small, an alert may beprovided and if the detected leakage is relatively large, the operator may beinstructed to go to a workshop immediately.

The step of detecting s102, s104 leakage in the hydraulic steering system 10based on a detected movement of the piston 22 caused by tyre hysteresis mayalso comprise determining the size of the leakage based on the speed of thepiston movement. The piston movement is defined as a distance. The largerthe leakage, the faster moves the piston 22. This is illustrated in the graphs ofFigure 5, showing the piston position P changing over time T when there is aleakage. The speed of the piston movement may be determined/calculated bydetermining the position P of the piston 22 over time. The piston position Pmay for example be measured for a predetermined period of time, and thepiston speed may be calculated based on the change of piston position P(piston movement) during this predetermined period of time. ln the example shown in Figure 5, the piston movement has been measuredfrom a first point in time t1 to a second point in time t2. During this detectingtime, the piston 22 will move from a first piston position PP1 to a second pistonposition PP2. The top graph shows an example where the leakage is relativelysmall. The piston movement S1 is the distance between the first piston positionPP1 and the second piston position PP2. The lower graph shows an examplewhere the leakage is relatively large. Compared to the top graph, the distanceS2 between the first piston position PP1 and the second piston position PP2 is now larger during the same period of time. Thus, with a larger leakage, the 24 piston will move a longer distance during the same period of time compared towhen the Ieakage is smaller. ln other words, a higher speed of the piston movement will indicate a larger Ieakage.

Typically, the piston 22 will move from the very second the wheel 6 has beensteered to the predetermined position P1, P2, until the hydraulic fluid 28 hasleaked so much that the pressure caused by the hysteresis force is negligible.Small leakages will thus require more detecting time than large leakages.Generally, the piston 22 will move faster in the beginning when the wheels 6have been steered and the hysteresis force starts acting on the piston 22. Thisis because the pressure in the chamber 24, 26 associated with the Ieakage islarger at the beginning, before the hydraulic fluid 28 has leaked out. Thus, inorder to determine the size of the Ieakage it may be suitable have a detectingtime between 15-30 seconds. As an example, a piston speed below a speedthreshold value may be considered a small Ieakage and a piston speed abovethe speed threshold value may be considered a large Ieakage. Alternatively,the control device 100 may comprise a look-up table or list of predeterminedpiston speeds and corresponding Ieakage sizes saved in a database, whereindetermining the size of the Ieakage comprises comparing the determinedpiston speed with the list. The Ieakage size may thus be determined by meansof data mapping. lf the size of the Ieakage is equal in both directions, that is, ifthe size of the Ieakage is equal on both sides of the piston 22, it may indicate that the Ieakage is in the piston seal 23.

Figure 6 is a diagram of a version of a device 500. The control device 100described with reference to Figure 2 may in a version comprise the device 500.The device 500 comprises a non-volatile memory 520, a data processing unit510 and a read/write memory 550. The non-volatile memory 520 has a firstmemory element 530 in which a computer programme, e.g. an operatingsystem, is stored for controlling the function of the device 500. The device 500further 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 counter and an interruption controller (not depicted). The non-volatile memory 520 has alsoa second memory element 540.

There is provided a computer programme P which comprises routines fordetecting Ieakage in a hydraulic steering system of a vehicle. The computerprogramme P further comprises routines for steering the wheels from a centreposition to a first predetermined position by controlling the piston in a firstdirection; and detecting Ieakage in the hydraulic steering system based on adetected movement of the piston in a second direction, opposite to the firstdirection, wherein any movement of the piston is detected by means of theposition sensor. The computer programme P may also comprise routines forsteering the wheels to a second predetermined position by controlling thepiston in the second direction; and detecting Ieakage in the hydraulic steeringsystem based on a detected movement of the piston in the first direction. Thecomputer programme P may also comprise routines for detecting Ieakagewhen the detected piston movement exceeds a predetermined thresholddistance. The computer programme P may also comprise routines fordetermining the size of the Ieakage based on the speed of the pistonmovement. The programme P may be stored in an executable form or in a compressed 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 theprogramme stored in the memory 560 or a certain part of the programmestored in the 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 withthe 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 data processing unit 510 via a data bus 514. 26 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 programme stored inthe memory 560 or the read/write memory 550. When the device 500 runs theprogramme, methods herein described are executed.

The foregoing description of the preferred embodiments of the presentinvention is provided for i||ustrative and descriptive purposes. lt is not intendedto be exhaustive or to restrict the invention to the variants described. Manymodifications and variations will obviously be apparent to one ski||ed 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 detecting Ieakage in a hydraulic steering system (10) of avehicle (1), the hydraulic steering system (10) comprising: a hydraulic cylinder (20) with a piston (22) movably arrangedinside the cylinder (20) forming a first chamber (24) and a second chamber(26) inside the cylinder (20); and a position sensor (30) arranged to determine the position of thepiston (22) inside the cylinder (20),wherein the piston (22) is connected to wheels (6) of a wheel axle (8), suchthat movement of the piston (22) will steer the wheels (6), the methodcomprising: steering (s101) the wheels (6) from a centre position (Pc) to a firstpredetermined position (P1) by controlling the piston (22) in a first direction(D1); and detecting (s102) Ieakage in the hydraulic steering system (10)based on a detected movement of the piston (22) in a second direction (D2),opposite to the first direction (D1), wherein any movement ofthe piston (22) is detected by means of the position sensor (30).

2. The method according to claim 1, further comprising: steering (s103) the wheels (6) to a second predetermined position(P2) by controlling the piston (22) in the second direction (D2); and detecting (s104) Ieakage in the hydraulic steering system (10)based on a detected movement ofthe piston (22) in the first direction (D1).

3. The method according to claim 2, wherein movement of the piston (22) inthe first direction (D1) indicates Ieakage in a first valve (52) arranged inassociation with the first chamber (24) of the cylinder (20).

4. The method according to any one of the preceding claims, wherein movement of the piston (22) in the second direction (D2) indicates Ieakage in 28 a second valve (54) arranged in association with the second Chamber (26) ofthe cylinder (20).

5. The method according to any one of the preceding claims, wherein Ieakageis detected when the detected piston movement exceeds a predeterminedthreshold distance.

6. The method according to c|aim 5, wherein the predetermined thresholddistance is within the range of 0,2-0,5 millimetres.

7. The method according to any one of the preceding claims, wherein detectingIeakage in the hydraulic steering system (10) comprises determining the sizeof the Ieakage based on the speed of the piston movement.

8. The method according to c|aim 3 and 4, wherein movement of the piston(22) in the first direction (D1) and the second direction (D2) indicates Ieakagein both the first valve (52) and the second valve (54) or Ieakage in a piston sea|(23) between the first chamber (24) and the second chamber (26).

9. A computer program (P) comprising instructions which, when the programis executed by a computer (100; 500), cause the computer (100; 500) to carryout the method according to any one of the preceding c|aims.

10. A computer-readable medium comprising instructions, which whenexecuted by a computer (100; 500), cause the computer (100; 500) to carryout the method according to any one of c|aims 1-8.

11. A control device (100) for detecting Ieakage in a hydraulic steering system(10) of a vehicle (1), the hydraulic steering system (10) comprising: a hydraulic cylinder (20) with a piston (22) movably arrangedinside the cylinder (20) forming a first chamber (24) and a second chamber(26) inside the cylinder (20); and 29 a position sensor (30) arranged to determine the position of thepiston (22) inside the cylinder (20),wherein the piston (22) is connected to wheels (6) of a wheel axle (8), suchthat movement of the piston (22) will steer the wheels (6), wherein the controldevice (100) is arranged in communication with the position sensor (30) and isconfigured to, after the wheels (6) have been steered from a centre position(Pc) to a first predetermined position (P1) by controlling the piston (22) in a firstdirection (D1), detect Ieakage in the hydraulic steering system (10) based ona detected movement of the piston (22) in a second direction (D2), opposite tothe first direction (D1), wherein any movement of the piston (22) is detected by means of the position sensor (30).

12. The control device (100) according to c|aim 11, wherein the control device(100) is configured to, after the wheels (6) have been steered to a secondpredetermined position (P2) by controlling the piston (22) in the seconddirection (D2), detect Ieakage in the hydraulic steering system (10) based ona detected movement of the piston (22) in the first direction (D1).

13. The control device (100) according to c|aim 11 or 12, wherein the controldevice (100) is configured to determine the size of the Ieakage based on thespeed of the piston movement.

14. The control device (100) according to any one of c|aim 11-13, wherein thecontrol device (100) is configured to steer the wheels (6) from the centreposition (Pc) to the first predetermined position (P1) by controlling the piston(22) in the first direction (D1).

15. A vehicle (1) with a hydraulic steering system (10), the hydraulic steeringsystem (10) comprising: a hydraulic cylinder (20) with a piston (22) movably arrangedinside the cylinder (20) forming a first chamber (24) and a second chamber(26) inside the cylinder (20); and a position sensor (30) arranged to determine the position of thepiston (22) inside the cylinder (20),wherein the piston (22) is connected to wheels (6) of a wheel axle (8) of thevehicle (1), such that movement of the piston (22) will steer the wheels (6),wherein the vehicle (1) further comprises a control device (100) according to any one of claims 11-14.