Method and system for controlling braking of a mining and / or construction machine

Abstract

The present disclosure relates to a method for controlling braking of a mining and / or construction machine an internal combustion engine (104) and at least one retarder brake system (110) for applying torque to at least one drive wheel (111-114) of the machine (100) The machine also comprises operator manoeuvrable adjusting means (131) for adjusting a maximum level of retarder brake torque to be applied by the retarder brake system (110), and operator manoeuvrable accelerator means (132) being manoeuvrable in a movement region (A-B) between a first end position (A) and a second end position (B) for requesting engine torque from the internal combustion engine (104). The method comprises, when a brake torque is to be applied by the at least one retarder brake system (110): applying a brake torque by the at least one retarder brake system (110), wherein the magnitude of the applied brake torque is dependent on the position of the accelerator means (132) in the movement region and the operator setting of the adjusting means (131).

Description

[0001]METHOD AND SYSTEM FOR CONTROLLING BRAKING OF A MINING AND / ORCONSTRUCTION MACHINEField of the disclosureThe disclosure relates in particular to mining, tunnelling and construction, and morespecifically to a method and a system for controlling braking of a mining and / orconstruction machine. The disclosure also relates to a computer program, a computer-readable medium and a mining and / or construction machine comprising a system.Background of the disclosureRock excavation, such as in mining, tunnelling and construction may be carried outusing various techniques, where, e.g., excavation using drilling and blastingtechnology is a commonly used method. The excavation is, in general, carried out ina manner in which drilling is performed in rounds, where a round of holes is drilled tothereafter be loaded with explosives to blast the rock.The broken rock is removed, and a new round of holes may be drilled to blast asubsequent portion of the rock. The excavation may generate large volumes ofbroken rock to be transported away, and mining and / or construction machines suchas dumpers, trucks, and LHD (load, haul, dump) machines may be utilized in thisregard. These machines are heavy and may be designed to carry loads, e.g., in theorder of 10-100 metric tonnes of load.Machines of this kind may be affected by gravity when travelling downhill in such away that the vehicle speed may increase in case a brake torque is not applied. Anoperator of this kind of machines may therefore utilize a brake system, such as awheel brake system, to control the speed of the vehicle to a desired speed whengoing downhill.However, with regard to, e.g., mining and / or construction machines, similar to othertypes of vehicles, extensive braking using wheel brakes should in general beavoided, and instead it is oftentimes preferred to as much as possible utilize one ormore retarder brake systems for braking the machine, in particular when goingdownhill. This is because there is a risk of overheating the wheel brake system incase the machine is continuously being driven downhill for extended periods of time.This may be the case, e.g., when travelling downwards in an underground mine.The wheel brake system may hence be relieved from excessive use through the useof one or more retarder brake systems to apply at least part of the requested braketorque instead of using the wheel brakes. Such retarder brakes may, e.g., compriseone or more from engine brake, exhaust brake, retarder brake. The activation of theretarder brake systems may be configured to be controlled by an operator bymaneuvering operator maneuverable means, such as a brake pedal and / or othermeans, e.g., a lever.Summary of the disclosureAn object of the present disclosure is to provide a method for controlling braking of amining and / or construction machine that provides for a retarder brake system usethat is highly adaptable to the presently prevailing driving conditions.According to a first aspect of the disclosure it is provided a method for controllingbraking of a mining and / or construction machine, the machine comprising:an internal combustion engine for providing propelling torque to at least one drive wheel of the machine, at least one retarder brake system for applying brake torque to at leastone drive wheel of the machine, operator manoeuvrable adjusting means for adjusting a maximum levelof retarder brake torque to be applied by the retarder brake system, operator manoeuvrable accelerator means for requesting engine torquefrom the internal combustion engine, the accelerator means being manoeuvrable in amovement region between a first end position and a second end position, the methodcomprising, when a brake torque is to be applied by the at least one retarder brake system: applying a brake torque by the at least one retarder brake system, wherein the magnitude of the applied brake torque is dependent on the position ofthe accelerator means in the movement region and the operator setting of theadjusting means.As was mentioned above, rock excavation may result in large amounts of brokenrock that needs to be transported away from the location of excavation, e.g., to alocation for further treatment. Such transportation is oftentimes carried out by miningand / or construction machines, where these machines may not only be heavy inthemselves, but also be designed to carry large amounts of load.Furthermore, the routes being used for transport of this kind oftentimes involveuphill / downhill driving, and in particular when going downhill braking of the machinemay be required to counteract the accelerating force of gravity. Although a wheelbrake system may be utilised, it is in general preferred to utilise a retarder brakesystem. A main reason for this is that wheel brake systems in general are frictionbased, and thereby subject to wear, and potentially to fatigue and thereby reducedbraking capability during extensive braking. Problems of this kind may be alleviatedusing a retarder brake system, since retarder brake systems allow prolonged usewhile still maintaining braking capabilities.However, although a retarder brake system may alleviate drawbacks of wheel brakesystems, and maintain a desired machine speed the driving conditions may vary,e.g., in terms of current machine load, and / or inclination of the surface upon whichthe machine is currently being driven.According to the disclosure, it is provided a method for a machine comprising aretarder brake system by means of which an operator of the machine may adapt theapplied brake force to variations in the driving conditions in a manner that providesfor a high driveability of the machine. The machine comprises an operatormanoeuvrable adjusting means, such as a knob, lever, display setting, or othersuitable adjusting means, for adjusting a maximum level of retarder brake torque tobe applied by the retarder brake system. That is, a retarder brake system of themachine may in general be capable of providing a predetermined maximum brake torque, where the maximum brake torque may be dependent on the drivingconditions and hence vary, e.g., in dependence of vehicle speed, speed of rotation ofan internal combustion engine etc. However, irrespective of such variations, theoperator manoeuvrable adjusting means allow the operator to change the maximumretarder brake torque to be applied in a current driving situation. The operator mayhence use the adjusting means to control the amount of retarder brake force that is tobe applied for a particular retarder brake torque request. Furthermore, the magnitude of the retarder brake torque to be applied is also partlydependent on the position of an operator manoeuvrable accelerator means, such asan accelerator pedal, for requesting engine torque from the internal combustionengine. This means that the magnitude of the applied brake torque is dependent onthe position of the accelerator means in the movement region, and the operatorsetting of the adjusting means. This provides for a solution that allows an operatorvary the retarder brake torque to be applied to a very high extent according topreferences and prevailing driving conditions. According to aspects of the disclosure, the magnitude of the brake torque being applied by the at least one retarder brake system is adjusted while a retarder braketorque is applied in response to an operator adjustment of the maximum level ofretarder brake torque to be applied by the retarder brake system using the operatormanoeuvrable adjusting means. Consequently, the operator may change the retarderbrake dependency during ongoing operation, so that the applied torque for a particular accelerator pedal position thereby will also change.According to aspects of the disclosure, a retarder brake torque of a magnitudecorresponding to the maximum level of retarder brake torque set by the adjustingmeans is applied when the accelerator means is fully released from a request fortorque. This means that the operator may simply release the accelerator means to obtain an applied retarder brake torque that corresponds to the set maximum to be applied. According to aspects of the disclosure, the magnitude of the applied retarder braketorque is adjusted in response to an operator adjustment of the maximum level ofretarder brake torque to be applied by the retarder brake system when theaccelerator means is fully released from a request for torque. This means that the operator may vary the applied retarder brake force as desired also when the accelerator means is fully released. According to aspects of the disclosure, a brake torque is applied from the at least one auxiliary brake system when the accelerator means is positioned in a first portion ofthe movement region of the accelerator means, and requesting a torque from theinternal combustion engine when the accelerator means is positioned in a secondportion of the movement region of the accelerator means. The accelerator meansmay hence be utilized to control both the applied brake torque as well as the applied propelling torque, where the control.According to aspects of the disclosure the magnitude of the brake torque to beapplied from the at least one auxiliary brake system, and the magnitude of the request for torque from the internal combustion engine, respectively, is configured to vary in dependence of the position of the accelerator means within the first portion of the movement region, and the second portion of the movement region of theaccelerator means, respectively. The accelerator means may hence be utilized tovary the applied brake torque by varying the accelerator position in the first portion ofthe movement region, and / or the applied propelling torque by varying the acceleratorposition in the second portion of the movement region. According to aspects of the disclosure, the position in the movement region of theaccelerator means at which the first portion of the movement region transitions to thesecond portion of the movement region, and vice versa, may vary in dependence of the current setting of the adjusting means for adjusting the maximum level of retarderbrake torque. Hence, for example, a larger portion of the movement region of theaccelerator means may be utilized for applying a retarder brake torque when themaximum level of retarder brake torque to be applied by the retarder brake system isset to a comparatively higher maximum brake torque than when the maximum level of retarder brake torque to be applied by the retarder brake system is set to acomparatively lower maximum brake torque. The accelerator position at which theapplying of a brake torque transitions to an applying of propelling torque may thereby be configured to vary substantially.According to aspects of the disclosure, the magnitude of the retarder brake torque tobe applied by the at least one retarder brake system is determined also independence of speed of rotation of the internal combustion engine. Consequently, asame setting of the operator manoeuvrable adjusting means for adjusting a maximum level of retarder brake torque, and a same position of the accelerator means may still give rise to varying retarder brake torque in dependence of the currently prevailing speed of rotation of the internal combustion engine. According to aspects of the disclosure, the retarder brake torque, or request for torque from the internal combustion engine, is determined in dependence of the position of the accelerator means according to the relation: ^= ^ − ^^ ∗ ^(^)(1 − ^), wherein^ is the torque to be applied, normalized to -1 for maximum retarderbrake torque and +1 for maximum engine torque; ^is the accelerator means position, normalized to vary from 0 for thefirst end position to 1 for the second end position; ^^is the setting of the adjusting means, normalized to vary from 0 for minimum retarder brake torque to be requested to 1 for the maximum possible retarder brake torque; ^(^) is a function of the speed of rotation (^) of the internal combustionengine. This provides a straight-forward method of realizing the control of the applied retarder brake torque according to the disclosure.The function ^(^) may, for example, be any from: a constant, a function proportionalto the speed of rotation (^) of the internal combustion engine, a function proportionalto an exponential of the speed of rotation (^) of the internal combustion engine. Incase ^(^) is a constant the equation reduces to a linear dependency.According to aspects of the disclosure, when torque is requested from the internalcombustion engine, movement of the accelerator means in the movement regiontowards the second end position increases the request for torque from the internal combustion engine towards the currently maximum deliverable torque of the internalcombustion engine. The accelerator means may hence function much as aconventional accelerator means, with the difference that the propelling torque request may be limited to only a portion of the movement region of the accelerator means. According to aspects of the disclosure, the adjusting means is configured to adjust the retarder brake torque between a minimum value and a maximum value of applicable retarder brake torque.According to aspects of the disclosure, the operator manoeuvrable acceleratormeans for requesting torque from the internal combustion engine is an acceleratorpedal, wherein the accelerator is moved in the movement region by depressing the accelerator pedal. According to aspects of the disclosure, the at least one retarder brake system comprises one or more from: a compression brake system, an exhaust brake system,a hydraulic retarder, a magnetic retarder. Hence, the machine may comprise variousdifferent retarder brake systems. Such systems are known in the art.According to aspects of the disclosure, the applied brake torque and propellingtorque, when manoeuvring the operator manoeuvrable accelerator means in themovement region, and for a particular setting of the operator manoeuvrable adjusting means, is controlled such that the applied torque changes continuously with acontinuous movement of the accelerator means. The applied torque may hence bechanged such that there is no abrupt changes in applied torque while manoeuvringthe accelerator means.According to a further aspect, the disclosure relates to a system for braking a miningand / or construction machine. It will be appreciated that all features described for themethod aspects of the disclosure are applicable also to the system aspects of thedisclosure. Also, the system and its aspects have advantages corresponding to theadvantages discussed above with regard to methods. The disclosure also relates to amining and / or construction machine comprising a system of such kind.Further advantageous embodiments of the disclosure will emerge from the detaileddescription. Brief description of the drawingsFigs. 1A-B illustrates an exemplary mining machine according to aspects of thedisclosure; Fig.1C schematically illustrates an accelerator pedal that can be used when controlling a retarder brake torque according to aspects of the disclosure;Fig. 2 schematically illustrates an exemplary method according to aspects of thedisclosure; Fig.3 schematically illustrates another exemplary method according to aspects of the disclosure; Fig.4 schematically illustrates an example of a dependency of applied retarder brake torque in relation to accelerator pedal position:Fig. 5 schematically illustrates a further example of a dependency of applied retarderbrake torque in relation to accelerator pedal position;Fig. 6 schematically illustrates an example of a dependency of applied retarder braketorque in relation to accelerator pedal position as well as speed of rotation of aninternal combustion engine; Fig.7 schematically illustrates a driving example utilizing aspects of the disclosure. Detailed description of embodimentsEmbodiments of the present disclosure will be exemplified in the following in view ofa particular example of a mine truck. The disclosure is, however, applicable for allkinds of mining and construction machines that fulfil the features specified in theindependent claims. For example, the disclosure is applicable for machinescomprising other types of containers than the illustrated dump box, such as, e.g.,front loaders etc.Fig. 1A illustrates a side view of an exemplary mine truck 100 which may beconfigured to operate according to the present disclosure. According to the presentexample, the mine truck 100 is designed for underground use, such as inunderground mines and tunnels. The mine truck 100 further constitutes an articulated machine, where a front portion 100a is connected to a rear portion 100b by means ofa hinge 101, and the mine truck 100 is consequently steered by means of articulatedsteering to facilitate manoeuvring. Mine trucks of the disclosed kind are often driven in surroundings where the distance to surrounding rock walls may be small, andarticulated machines may provide advantages in manoeuvrability over non-articulatedmachines in such environments. As is appreciated by the person skilled in the art, theillustrated mine truck merely forms an example of usability of the disclosure, and, inprinciple, the disclosure is applicable for essentially any kind of mine truck and alsoother types of mining and / or construction machines.The mine truck 100 is utilised to load and transport away materials, such as, e.g.,excavated rock through the use of a container 115 for carrying the payload, thecontainer 115 commonly being denoted dump box. The mine truck 100 alsocomprises front axle wheels 111, 113 and rear axle wheels 112, 114, where part ofthe wheels are illustrated in Fig. 1B, to allow the truck 100 to be driven betweendifferent locations of the mine / tunnel. The truck also comprises an operator cabin 102 for truck operation by an onboard operator, i.e., driver of the machine. The operatorcabin 102 may comprise various operator controllable means, such as one or morejoysticks, and / or one or more displays for use in the operator control of the mine truck100. There may also be present accelerator means such as an accelerator pedal132, and also a brake pedal 138. Also, in particular according to the presentdisclosure, there may be operator manoeuvrable adjusting means 131, such as aknob or lever, through the use of which the operator may adjust the maximum level ofretarder brake force that the machine control system is to apply when a retarderbrake force is requested. There may also exist various additional means for allowingthe operator to request various actions to be taken by the mine truck, such as, e.g.,buttons, keyboards, switches etc. The operator cabin may also comprise further and / or other types of operator controllable means. The mine truck 100 further comprises a machine control system comprising at leastone control unit 130. The control unit 130 is configured to control various of thefunctions of the truck 100, where the control unit 130 may receive control signalsfrom the operator through the operator controllable means requesting various actions to be taken, and where the control signals, such as operator inflicted joystick deflections and / or manoeuvring of other means may be translated by the controlsystem to suitable control commands. The control unit 130 may, for example, beconfigured to request motions to be carried out by various actuators such ascylinders / motors / pumps etc., e.g., for manoeuvring the mine truck, e.g., in terms ofsetting the truck in motion, and / or controlling the joint 101 to steer the machine100.The control unit 130 may also be utilised, e.g., to control various equipment of themine truck 100 on the basis of signals from operator controllable means, such asrequest for accelerating torque or brake torque.Trucks of the disclosed kind may comprise more than one control unit, e.g., a pluralityof control units, where each control unit, respectively, may be arranged to beresponsible for monitoring and carrying out different functions of the truck 100. Forreasons of simplicity, however, it will be assumed in the following that the various functions are controlled by the control unit 130.Control systems of the disclosed kind may further comprise a data bus 140, whichmay, e.g., be a CAN bus, or any other suitable kind of data bus, and which may beused to allow communication between various units of the machine 100, and whichmay utilise, e.g., CANopen safety protocol or any other suitable protocol in thecommunication. The CAN bus 140 may be utilized to connect the accelerator pedal sensor 135 and driver adjustable means 131 to the control unit 130.Fig. 1B further shows a power source 104 in the form of an internal combustionengine, an exhaust brake 105, a gearbox 106 and a retarder 110. The figure alsoillustrates a propeller shaft 107 powering the wheels using the internal combustionengine 104, and wheel brakes 120. The retarder brake system is used to relieve thewheel brakes 120 from extensive use, to thereby prevent overheating and reducedbraking capabilities. As was mentioned above, according to embodiments of the disclosure, it is an objectto provide a method for controlling braking of the machine, such as, for example, amachine of the kind disclosed in Figs.1A-B.An exemplary method 200 according to the disclosure will be briefly described withreference to Fig. 2, and more in detail with reference to the method in Fig. 3.According to step 201 of the method in Fig. 2, a retarder brake torque is applied independence on the accelerator position, and the operator setting of the adjustingmeans 131.As was mentioned above, mine trucks may be of very large dimensions and exhibitsubstantial mass, in particular when carrying payload, where the mine truck may bedesigned to carry, e.g., up to 50-100 tonnes of broken rock or more. Thereby, thetruck is subjected to a substantial impact from the force of gravity when going uphillor downhill, where, when the machine is traveling downhill, the force of gravity maysubject the machine to a substantial accelerating force. An operator of the machinewill therefore have to apply a brake force in order to prevent the machine fromaccelerating to higher than desired speeds. This may, in general, be accomplishedthrough the use of a brake pedal where the operator, through suitable depression ofthe brake pedal, may request a brake torque that provides a desired braking of themachine. The applied brake torque is in general provided by a retarder brake systemfor the reasons stated above, where the retarder brake system may comprise one ora combination of various different retarder brakes. For example, the machine maycomprise a retarder brake system comprising one or more from: a compression brake system, an exhaust brake system, a hydraulic retarder, a magnetic retarder. Such retarder brake systems are known per se and are therefore not described more in detail. The retarder brake torque being applied according to aspects of the disclosure may be a combined torque from one or more such retarder brake systems.According to the present disclosure, instead of utilizing a brake pedal, operatormanoeuvrable accelerator means, such as the accelerator pedal 132, are used torequest a desired brake force. According to the disclosure, the accelerator pedal 132is used both to request a propelling torque from the internal combustion engine 104of the machine 100, and also to request a retarder brake torque, where the resultingtorque (brake torque or propelling torque) depends partly on the current position ofthe accelerator pedal 132, and also partly on the operator manoeuvrable adjustingmeans 131 for adjusting the maximum level of retarder brake torque to be applied bythe retarder brake system. A fully released accelerator pedal 132 may indicate arequest for a maximum retarder brake torque, where the current maximum retarderbrake torque, in turn, is determined by the maximum retarder brake torque as set bythe operator using the adjusting means 131. The brake torque being applied whenthe accelerator pedal 132 is fully released will hence depend on the current setting ofthe adjusting means 131.Furthermore, the more the accelerator pedal 132 is depressed from the fully releasedstate, the less brake torque may be applied until the accelerator pedal has been depressed to an extent where no brake torque at all is applied, and where, wheneven further depressing the accelerator pedal, a propelling torque from the internalcombustion engine 104 is instead requested, where the requested propelling torqueincreases the more the accelerator pedal 132 is depressed.Fig. 1C illustrates an exemplary operator manoeuvrable accelerator means forrequesting torque in the form of the accelerator pedal 132. The figure illustrates theactual accelerator pedal 132, which is movable in a movement region between a fullyreleased state, indicated by dashed line “A”, and a fully depressed state, indicated bydashed line “B”.The figure also illustrates that the accelerator pedal 132 currently is depressed to anextent represented by depression angle “X”, where the current state of theaccelerator pedal 132, e.g., may be determined using an angle sensor such as anglesensor 135. It is to be understood that according to the present example, theaccelerator pedal 132 is not physically linked, e.g., to means for requesting torquefrom the internal combustion engine 104. Instead, signals from the angle sensor 135 indicating the current accelerator pedal position is used by the machine controlsystem to request torque from the internal combustion engine, or the retarder brakesystem, in a variable dependency of the current position. Fig. 1C also illustrates adotted line 133, which may exemplify the position at which the requested torquetransitions from a request for brake torque to a request for propelling torque. That is,when the brake pedal, as in the present state of Fig. 1C, is within the depressionangle denoted α, a brake torque will be applied whereas, when the accelerator pedalis depressed to a state within the angular interval indicated by angled β propellingtorque is instead requested from the internal combustion engine 104.According to the present disclosure, the actual torque being applied by the retarderbrake system will hence depend not only on the accelerator pedal position, but alsoon the current setting of the operator manoeuvrable adjusting means 131 foradjusting the maximum retarder brake torque to be applied. A particular depressionof the accelerator pedal, such as the situation illustrated in Fig. 1C, may thereforeresult in various different brake torque, or propelling torque, requests, where thetorque request for a particular accelerator position may change as soon as theoperator changes the maximum brake torque to be applied using the adjustingmeans 131.This will be further explained with reference to the method 300 of Fig. 3, and Figs. 4-7 below.The method 300 starts in step 301, where the current position of the acceleratorpedal 132 is determined. This can, for example, and as was explained, bedetermined using signals from angle sensor 135 in Fig. 1C, where the signals fromthe angle sensor 135 indicates the current position of the accelerator pedal 132. The method then continues to step 302 where it is determined a current setting of theoperator manoeuvrable adjusting means 131 for adjusting the maximum retarderbrake torque to be applied. This may be determined, similar to the accelerator pedal,e.g., using an angle sensor in case the operator adjustable means consists of aknob, or any other suitable means for determining the operator setting depending onthe particular means being used to realize the adjusting possibilities. According toaspects, e.g., a slider or similar on a display may also be used. Following step 302 the torque to be applied, whether this torque is an engine, andhence propelling, torque or a brake torque, is determined in step 304. Thisdetermination may be carried out in various different ways. A first example isillustrated in Fig. 4. Fig. 4 shows on the y-axis the resulting request for torque τ,where positive values (> 0) indicate a request for engine torque and negative values(<0) indicate a request for brake torque. The dotted horizontal line 410 represents arequest for zero torque, and hence no retarder torque or propelling torque. Therequests for propelling (engine) torque increases with increasing positive values onthe y-axis, and brake torque increases with increasingly negative values on the y-axis. It is to be noted that the actual torque values have been normalized so that “1”on the y-axis in the figure represents a request for full engine torque, and “-1” on they-axis in the figure represents a request for full retarder brake torque.The x-axis, in turn, represents pedal position, where the leftmost position in the figureindicates a fully released accelerator pedal and the rightmost position indicates a fullydepressed accelerator pedal. The pedal position, too, is illustrated as beingnormalized between “0” (fully released) and “1” (fully depressed). The figure furtherillustrates solid lines 401 and 402, which represents a minimum setting and maximumsetting, respectively, of the operator adjustable means in terms of request for retarderbrake torque.When the operator adjustable means is set to zero request for retarder brake torquethe characteristics, according to the present example, of the torque request in relationto accelerator pedal position will follow the line 401. That is, zero brake torque will beapplied for a fully released accelerator pedal, and where the request for propellingtorque will continuously increase as the accelerator pedal is depressed from zerodepression until fully depressed. This hence corresponds to conventional operationof an accelerator pedal. On the other hand, when the maximum allowable braketorque is set to the maximum possible retarder brake torque, the characteristic of theaccelerator pedal will, instead, follow line 402. This means that a fully releasedaccelerator pedal, point 402A, will provide a retarder brake torque being themaximum possible retarder brake torque.If the accelerator pedal 132 is then depressed, the applied retarder brake torque willdecrease as the accelerator pedal is further depressed. A brake torque, thoughcontinuously reducing, will continue to be applied until the accelerator pedal hasbeen depressed approximately halfway down, point 404, pedal position “PA”, wherethe applied brake torque has reduced to zero. Further depression of the acceleratorpedal, i.e., beyond position “PA” will, instead, result in a request for a propellingtorque that increases with continued depression of the accelerator pedal, and wherea fully depressed accelerator pedal again results in a maximum propelling torquerequested from the internal combustion engine 104.According to aspects of the disclosure, the operator adjustable means provide forcontinuous variation of the setting between the minimum value and maximum valueof the retarder brake torque, which may hence be continuously adjusted using theoperator adjusting means. This may result in a torque dependency according to anypossible line ending at 403 (maximum requested propelling torque, fully depressed accelerator pedal, and starting at any point between the points 401A and 402A. Thetorque characteristic when depressing the accelerator pedal may hence essentiallyfollow any line starting between 401A and 402A and ending in point 403. This isexemplified with dashed line 406, which hence only is one example out of many, andwhich represents a setting of approximately 50% of the total retarder brake torque tobe applied when the accelerator is fully released. Following depression of theaccelerator, similar to before, the applied brake torque decreases with the degree ofdepression of the accelerator, and in this case zero brake torque is reached atapproximately 33% depression of the accelerator pedal, point 405, acceleratorposition “PB”. Again, further depression from point 405 results in a request forpropelling torque that increases towards point 403 the more the accelerator isdepressed. In case the operator adjustable means has a number of distinct settingsinstead of being continuously variable this would be represented by a correspondingnumber of lines starting between 401A and 402A and ending in 403 in Fig.4. Following the determination of the torque to be applied in step 304, the method continues to step 305, where it is determined whether a brake torque is to be applied, in which case the determined retarder brake torque is applied in step 306. The method then returns to step 301 to repeat the determination. In case no retarderbrake torque is to be applied engine torque is instead requested in step 307, wherethe requested torque may be zero torque, following which the method returns to step301, again to repeat the determination. In this way the applied torque is continuously applied according to the current settings.According to the example of Fig. 4, a linear relationship between accelerator positionand request for torque is utilized. This need not be the case but that a relationshipmay also be non-linear. This is exemplified in Fig. 5, which is similar to Fig. 4 but withthe difference that the torque pedal position relationship is, instead, nonlinear, andwhere the applied torque may follow essentially any line starting between 501A and502A and ending in point 503 in Fig.5. According to a further example, the relationship of applied torque is, in addition, dependent on the current engine speed. This will be exemplified in the following. Forexample, the relationship of applied torque τ may, according to aspects of thedisclosure, follow the equation: ^= ^ − ^^ ∗ ^(^)(1 − ^), (eq. 1)Where: ^represents the torque to be applied, normalized to -1 for maximumretarder brake torque and +1 for maximum engine torque, i.e. similar to the illustration in figs.4-5. ^represents the accelerator pedal 132 position, also normalized asabove to vary from 0 for a fully released pedal to 1 for a fully depressed pedal.^^ represents the setting of the adjusting means 131, normalized to varyfrom 0 for minimum retarder brake torque to be requested to 1 for the maximum possible retarder brake torque; ^(^) is a function of the speed of rotation (^) of the internal combustionengine 104. The function ^(^) may, for example, be any function related to thespeed of the internal combustion engine, such as a speed dependent constant, afunction proportional to the speed of rotation (^) of the internal combustion engine104, a function proportional to an exponential of the speed of rotation (^) of theinternal combustion engine 104. For example, in case the accelerator pedal is fully released, the applied torquebecomes −^^ ∗ ^(^) since ^ in this case is zero. On the other hand, in case theaccelerator is fully depressed, ^=1, the resulting torque ^ = ^, i.e., maximumpropelling torque. Furthermore, since the dependency can be dependent not only on the acceleratorposition, and the setting of the operator manoeuvrable means, but also on the speedof rotation of the internal combustion engine, this provides for a considerablevariation in the control of the retarder brake system. The method of Fig. 3 includes anoptional step 303 in this regard, where the speed of rotation of the internalcombustion engine is determined. Fig. 6 illustrates an exemplary relationship oftorque-speed-accelerator position, where the general functionality is similar to what has been described for Fig.4, but where the additional dependency on the speed ofrotation of the internal combustion engine 104 is also disclosed. This means that thedependency no longer is two-dimensional, but three-dimensional.This is schematically illustrated by the 3D-graph in Fig. 6, which illustrates pedalposition on the x-axis, engine speed on the y-axis and resulting torque on the z-axis,where, e.g., the curves in Fig. 5 can be seen as different curves for a particularvehicle speed of rotation on the y-axis in Fig. 6. It is also to be noted that eachindividual setting of the operator adjustable means 131 will give rise to an individual 3D graph of the kind illustrated in fig.6 when the torque to be applied is also speed dependent.The disclosure consequently allows that the brake torque to be applied, also for afully released accelerator pedal, may be adjusted by the operator so that themaximum brake torque being applied is adapted to the currently prevailing drivingconditions, and where the brake torque can be adapted to, for example, currentinclination of the surface on which the machine currently is traveling and the currentload of the machine. As has been illustrated in Figs. 4-6 the accelerator pedalcharacteristic in regard of applied brake torque / propelling torque can be set to verydifferent characteristics, and thereby also allowing adjustment in accordance withdifferent operator preferences. As can also be seen in Figs. 4-6, the applied torquemay change continuously with a continuous change in accelerator pedal position.Furthermore, the operator adjustable means 131 for setting the maximum braketorque to be applied may also be used by the operator to continuously vary themaximum brake torque to be applied in dependence of currently prevailingconditions. This is exemplified in Fig. 7. Fig. 7 illustrates an exemplary drivingexample, where the upper graph illustrates road inclination and the lower graphillustrates the setting of the operator adjustable means, where “zero” represents zerorequest for brake torque when the accelerator pedal is fully released, and “max“represents maximum possible brake torque to be applied when the accelerator pedalis fully released.According to the illustrated example, the machine 100 travels on essentially levelground from times T0 to T1, and therefore the operator has set the maximum retarderbrake torque to be applied for a fully released accelerator pedal to essentially zero. Attime T1, or at some time before T1, the operator commences an increase of themaximum retarder brake torque to be applied when the accelerator pedal is fullyreleased, since the machine is about to enter a downhill slope. The operatorsuccessively increases the brake torque to be applied between times T1 and T2,since at time T2 the slope becomes relatively steep and the operator thereforerequests maximum retarder brake torque to be applied in case the accelerator pedalis released, and maintains this setting until approximately time T3, where the slopelevels out, and the operator therefore substantially reduces the retarder brake torqueto be applied to a relatively low level until time T4, where again the slope becomesmore steep and the operator therefore increases the maximum retarder brake torque to be applied when the accelerator is released, and then maintains this setting since the downhill slope continues.In this way, the operator may manoeuvre the machine through the downhill slopeessentially using the operator adjustable means for changing the applied braketorque and hence, e.g., with the accelerator, as well as brake pedal, fully released.This provides for a comfortable way of manoeuvring the machine that is alsobeneficial from a wheel brake wear point of view, since use of conventional wheelbrakes may be further reduced.A further example in regard of brake torque control is a case where the machine, forexample, is traveling downhill in a mine, where the machine may first be travelingdownhill in an unloaded state or with a lighter load. The maximum brake torque thatis required to operate a machine in a desired manner in this situation may becomparatively lower. In case the machine, during the downhill travel, stops to take onload, and thereby continue the downhill travel in a substantiality heavier state thanbefore, a considerably higher brake torque may be required in order to provide similardriving behaviour as before the additional load was taken on. The disclosure providesfor such a solution.Finally, the disclosure is not limited to the above-described aspects, but thedisclosure relates to, and encompasses, all of the different aspects that are includedwithin the scope of the independent claims.

Claims

Claims1. A method for controlling braking of a mining and / or construction machine (100), themachine (100) comprising:an internal combustion engine (104) for providing propelling torque to atleast one drive wheel (111-114) of the machine (100),at least one retarder brake system (110) for applying brake torque to atleast one drive wheel (111-114) of the machine (100),operator manoeuvrable adjusting means (131) for adjusting a maximumlevel of retarder brake torque to be applied by the retarder brake system (110),operator manoeuvrable accelerator means (132) for requesting enginetorque from the internal combustion engine (104), the accelerator means (132) beingmanoeuvrable in a movement region (A-B) between a first end position (A) and asecond end position (B), the method comprising, when a brake torque is to beapplied by the at least one retarder brake system (110): applying a brake torque by the at least one retarder brake system (110),wherein the magnitude of the applied brake torque is dependent on the position ofthe accelerator means (132) in the movement region and the operator setting of theadjusting means (131).

2. A method according to claim 1, further comprising, while a retarder brake torque is applied: adjusting the magnitude of the brake torque being applied by the at leastone retarder brake system (110) in response to an operator adjustment of themaximum level of retarder brake torque to be applied by the retarder brake system(110) using the operator manoeuvrable adjusting means (131).

3. A method according to claim 1 or 2, further comprising, when the acceleratormeans is fully released from a request for torque:applying a retarder brake torque of a magnitude corresponding to themaximum level of retarder brake torque set by the adjusting means (131).

4. A method according to any one of the claims 1-3, further comprising, when the accelerator means (132) is fully released from a request for torque: adjusting the magnitude of the applied retarder brake torque in responseto an operator adjustment of the maximum level of retarder brake torque to beapplied by the retarder brake system (110).

5. A method according to any one of the claims 1-4, further comprising,applying a brake torque from the at least one auxiliary brake system(110) when the accelerator means (132) is positioned in a first portion (α) of the movement region (A-B) of the accelerator means (132), and requesting a torque from the internal combustion engine (104) when theaccelerator means (132) is positioned in a second portion (β) of the movement region(A-B) of the accelerator means (132).

6. A method according to claim 5, wherein the magnitude of the brake torque to beapplied from the at least one auxiliary brake system (110), and the magnitude of therequest for torque from the internal combustion engine (104), respectively, is configured to vary in dependence of the position of the accelerator means (132)within the first portion (α) of the movement region (A-B), and the second portion (β) ofthe movement region (A-B) of the accelerator means (132), respectively.

7. A method according to claim 5 or 6, further comprising:changing the position in the movement region (A-B) of the accelerator means (132) at which the first portion (α) of the movement region (A-B) transitions to the second portion (β) of the movement region (A-B), and vice versa, in dependence of the current setting of the adjusting means (131) for adjusting the maximum level of retarder brake torque.

8. A method according to any one of the preceding claims, further comprising: when applying the brake torque by the at least one retarder brakesystem (110), determining the magnitude of the applied brake torque also independence of the speed of rotation of the internal combustion engine (104).

9. A method according to any one of the preceding claims, wherein the retarder braketorque, or request for torque from the internal combustion engine (104), independence of the position of the accelerator means (132) is determined accordingto the relation:^ = ^ − ^^ ∗ ^(^)(1 − ^), wherein^ is the torque to be applied, normalized to -1 for maximum retarderbrake torque and +1 for maximum engine torque; ^is the accelerator means (132) position, normalized to vary from 0 forthe first end position (A) to 1 for the second end position (B);^^is the setting of the adjusting means, normalized to vary from 0 forminimum retarder brake torque to be requested to 1 for the maximum possibleretarder brake torque; ^(^) is a function of the speed of rotation (^) of the internal combustionengine (104).

10. A method according to claim 9, wherein ^(^) is any from: a constant, a functionproportional to the speed of rotation (^) of the internal combustion engine (104), afunction proportional to an exponential of the speed of rotation (^) of the internalcombustion engine (104).

11. A method according to any one of the preceding claims, wherein, when torque isrequested from the internal combustion engine (104), movement of the acceleratormeans (132) in the movement region (A-B) towards the second end position (B)increases the request for torque from the internal combustion engine (104) towardsthe currently maximum deliverable torque of the internal combustion engine (104).

12. A method according to any one of the preceding claims, wherein the adjusting means (131) is configured to adjust the retarder brake torque between a minimum value and a maximum value of applicable retarder brake torque.

13. A method according to any one of the preceding claims, wherein the operatormanoeuvrable accelerator means for requesting torque from the internal combustionengine is an accelerator pedal, wherein the accelerator is moved in the movementregion (A-B) by depressing the accelerator pedal.

14. A method according to any one of the preceding claims, wherein the at least oneretarder brake system (110) comprises one or more from: a compression brakesystem, an exhaust brake system, a hydraulic retarder, a magnetic retarder.

15. A method according to any one of the preceding claims, further comprising, for aparticular setting of the operator manoeuvrable adjusting means:controlling the brake torque and propelling torque applied whenmanoeuvring the operator manoeuvrable accelerator means in the movement regionsuch that the applied torque changes continuously with a continuous movement ofthe accelerator means.

16. A system for braking a mining and / or construction machine comprising:an internal combustion engine (104) for providing propelling torque to at least one drive wheel (111-114) of the machine (100), at least one retarder brake system (110) for applying brake torque to atleast one drive wheel (111-114) of the machine (100), operator manoeuvrable adjusting means (131) for adjusting a maximumlevel of retarder brake torque to be applied by the retarder brake system (110), operator manoeuvrable accelerator means (132) for requesting enginetorque from the internal combustion engine (104), the accelerator means (132) being manoeuvrable in a movement region (A-B) between a first end position (A) and asecond end position (B), the system comprising means for, when a brake torque is tobe applied by the at least one retarder brake system (110): applying a brake torque by the at least one retarder brake system (110), wherein the magnitude of the applied brake torque is dependent on the position ofthe accelerator means (132) in the movement region and the operator setting of theadjusting means (131).

17. A mining and / or construction machine comprising a system according to claim 16.

18. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any one of the claims 1 to 15.

19. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of the claims 1 to 15.

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