WO2016099340A1 - A method for controlling a working machine during unloading - Google Patents

A method for controlling a working machine during unloading Download PDF

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Publication number
WO2016099340A1
WO2016099340A1 PCT/SE2014/000150 SE2014000150W WO2016099340A1 WO 2016099340 A1 WO2016099340 A1 WO 2016099340A1 SE 2014000150 W SE2014000150 W SE 2014000150W WO 2016099340 A1 WO2016099340 A1 WO 2016099340A1
Authority
WO
WIPO (PCT)
Prior art keywords
wheel axle
working machine
unit
frame unit
suspension arrangement
Prior art date
Application number
PCT/SE2014/000150
Other languages
French (fr)
Inventor
Mikael Petersson
Original Assignee
Volvo Construction Equipment
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Volvo Construction Equipment filed Critical Volvo Construction Equipment
Priority to PCT/SE2014/000150 priority Critical patent/WO2016099340A1/en
Publication of WO2016099340A1 publication Critical patent/WO2016099340A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G11/00—Resilient suspensions characterised by arrangement, location or kind of springs
    • B60G11/26—Resilient suspensions characterised by arrangement, location or kind of springs having fluid springs only, e.g. hydropneumatic springs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G17/00—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load
    • B60G17/005—Suspension locking arrangements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G17/00—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load
    • B60G17/015—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements
    • B60G17/017—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements characterised by their use when the vehicle is stationary, e.g. during loading, engine start-up or switch-off
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60P—VEHICLES ADAPTED FOR LOAD TRANSPORTATION OR TO TRANSPORT, TO CARRY, OR TO COMPRISE SPECIAL LOADS OR OBJECTS
    • B60P1/00—Vehicles predominantly for transporting loads and modified to facilitate loading, consolidating the load, or unloading
    • B60P1/04—Vehicles predominantly for transporting loads and modified to facilitate loading, consolidating the load, or unloading with a tipping movement of load-transporting element
    • B60P1/045—Levelling or stabilising systems for tippers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2300/00—Indexing codes relating to the type of vehicle
    • B60G2300/09—Construction vehicles, e.g. graders, excavators

Definitions

  • the present invention relates to a method for controlling a working machine.
  • the invention also relates to a control unit configured to control a working machine.
  • the invention is applicable on vehicles, in particularly working machines such as articulated haulers. Although the invention will mainly be described in relation to an articulated hauler, it is also applicable for other vehicles having a dump body for loading and unloading of material.
  • a full suspension articulated vehicle comprises an individual suspension arrangement for each of the wheels of the working machine, thus providing efficient and comfortable suspension of the articulated vehicle.
  • the articulated vehicle further comprises a tractor unit at which an operator cabin is provided, and a trailer unit provided with a dump body for loading material to be transported.
  • the dump body is connected to a frame unit of the trailer unit and can be raised and lowered by tilting the dump body in relation to the frame unit, which most often is executed by using hydraulic tilting cylinders such that the material in the dump body can be unloaded to a position rearward of the articulated vehicle.
  • the tractor unit and the trailer unit of the articulated vehicle are often pivotally connected to each other by a joint arrangement allowing mutual rotation of the tractor unit and the trailer unit around a geometric axis having a horizontal component in the longitudinal direction of the articulated vehicle.
  • the articulated vehicle is able to manage the rough terrain that is often associated to construction sites.
  • the object is at least partly achieved by the method for controlling a working machine according to claim 1.
  • a method for controlling a working machine comprising a front wheel axle and a rear wheel axle connected to a frame unit of the working machine at a distance from each other in a longitudinal direction of the working machine, the front wheel axle being connected to the frame unit by a front hydraulic wheel axle suspension arrangement and the rear wheel axle being connected to the frame unit by a rear hydraulic wheel axle suspension arrangement, wherein the method comprises the steps of receiving a signal indicative of an unloading mode of operation for the working machine; and fixating a distance in vertical direction between the rear wheel axle and the frame unit in response to the received signal.
  • the wording "fixating a distance in the vertical direction” should in the following and throughout the entire description be interpreted as a fixation of the distance between the wheel axle and the frame unit.
  • the distance is not needed to be vertical at all possible positions of the working machine as seen from a global coordinate system of the working machine.
  • the distance between the wheel axle and the frame unit may be vertical, but if the working machine is standing in a slope, the distance between the wheel axle and the frame unit is vertical as seen from the inclination of the slope onto which the working machine is positioned.
  • the rear hydraulic wheel axle suspension arrangement is connected between the rear wheel axle and the frame unit with an inclination.
  • the rear hydraulic wheel axle suspension arrangement is positioned with an inclination and is not fully vertical. In these situations, the distance between the front wheel axle and the frame unit should still be considered to be fixated in the vertical direction in response to the received signal.
  • the working machine comprises a hydraulic suspension arrangement on each side of the wheel axles, i.e. on each side of the frame as seen in the longitudinal direction of the working machine.
  • the rear wheel axle comprises a hydraulic suspension arrangement on each side thereof, such that the wheels on each side of the rear wheel axle comprise an individual hydraulic suspension arrangement, thereby making the vehicle a full suspension working machine.
  • the front wheel axle should be interpreted as a front wheel axle of the trailer unit.
  • the trailer unit comprises two wheel axles.
  • the signal indicative of an unloading mode of operation for the working machine should be interpreted as a signal indicating that the working machine is either intended to unload material from a dump body of the working machine, or is currently unloading the material with an indicated increased risk of lifting the working machine above the ground.
  • the unloading mode may be an upcoming event or an already ongoing event. Details and examples of the unloading mode of operation are given below in relation to example embodiments of the present invention.
  • the tipping point, or tipping axis, of the working machine is moved from a position located at a position between the front wheel axle and the rear wheel axle, back to a position located approximately at the rear wheel axle as seen from a longitudinal direction of the working machine. More specifically, the tipping point is moved rearwards to the position where the wheels of the rear wheel axle are in contact with the ground surface.
  • the tipping point should be understood to mean a position of the working machine around which the working machine can be unintentionally pivoted during unloading thereof.
  • the rear hydraulic wheel axle suspension arrangement may be positioned in a lock-up mode for preventing a relative motion between the rear wheel axle and the frame unit.
  • the rear hydraulic wheel axle suspension arrangement provides no damping between the rear wheel axle and the frame unit which provides an un-elastic connection between the ground and the frame via the rear hydraulic wheel axle suspension arrangement.
  • This un-elastic, non-damping, connection between the ground and the frame unit further secures that the tipping point is moved rearwards of the working machine.
  • the lock-up mode may be provided in many different ways which will be described further below.
  • the flow of hydraulic fluid of the rear hydraulic wheel axle suspension arrangement may be controlled.
  • hydraulic fluid may, for example, be prevented from being supplied to, or drained from, the rear hydraulic wheel axle suspension arrangement which will provide a "stiff connection between the rear wheel axle and the frame unit, i.e. the rear hydraulic wheel axle suspension arrangement has no damping characteristics.
  • hydraulic fluid may be prevented from being drained from the rear hydraulic wheel axle suspension arrangement.
  • a "stiff connection" is provided between the rear wheel axle and the frame unit. Prevention of hydraulic fluid drainage may be accomplished by using valve arrangements positioned in fluid communication with the hydraulic wheel axle suspension arrangement.
  • the rear hydraulic wheel axle suspension arrangement and the front hydraulic wheel axle suspension arrangement may be compressed to a maximum compression state thereof, respectively.
  • maximum compression state should be understood to mean a state of the hydraulic suspension arrangement where the suspension arrangement is compressed to an approximately maximum limit, at which no further compression is possible.
  • the rear hydraulic wheel axle suspension arrangement does not have any damping characteristics and the tipping point will thus be moved rearwards of the working machine. Hence, it is further secured that the rear wheel axle carries load so that the tipping point is located at the rear wheel axle.
  • a further advantage is that both the front and the rear hydraulic wheel axle suspension arrangements can be compressed approximately simultaneously.
  • front and rear hydraulic wheel axle suspension arrangements can be controlled simultaneously without the need of separately controlling each of the suspension arrangements and still displacing the tipping point backwards.
  • Another advantage is that the working machine does not have to rely on valves preventing hydraulic fluid from being drained from the rear hydraulic wheel axle suspension arrangement. Conversely, the present embodiment relies on the fact that hydraulic fluid should be drained from the rear hydraulic wheel axle suspension arrangement.
  • Positioning the rear hydraulic suspension arrangement in a maximum compression state may be executed by e.g. controlling the piston of the rear hydraulic wheel axle suspension arrangement to be positioned at an end position within a hydraulic cylinder thereof, or as according to another example embodiment, the rear hydraulic wheel axle suspension arrangement may be compressed such that a portion of the rear wheel axle and a portion of the frame unit are in abutment with each other.
  • portions of the rear wheel axle and the frame unit may be portions which are connected to the respective rear wheel axle and the frame unit.
  • the portion of the rear wheel axle may be a bracket or the like which is connected to the rear wheel axle.
  • the portion of the frame unit may also be a bracket or the like which is connected to the frame unit.
  • Other examples are of course also conceivable.
  • the signal indicative of the unloading mode of operation of the working machine may be received from a dump body tilting cylinder sensor arranged to detect actuation of a tilting cylinder of a dump body connected to the frame unit, wherein the working machine is determined to be in the unloading mode of operation if the dump body tilting cylinder sensor detects that the tilting cylinder is actuated.
  • the dump body tilting cylinder sensor detects that unloading is initiated, i.e. the dump body is starting to rise for unloading the material located therein.
  • the dump body tilting cylinder sensor may be positioned on the tilting cylinders for detecting when the tilting cylinders start to move.
  • the working machine may further comprise a tractor unit and a trailer unit comprising the frame unit, wherein the signal indicative of the unloading mode of operation of the working machine may be received from a load pressure sensor arranged to measure the load pressure on a wheel axle of the tractor unit, wherein the working machine is determined to be in the unloading mode of operation if the measured load pressure on the wheel axle of the tractor unit is below a predetermined pressure threshold level.
  • the load pressure sensor may be positioned on the wheel axle of the tractor unit.
  • the load pressure sensor may be positioned in connection to the hydraulic wheel axle suspension arrangement of the wheel axle of the tractor unit to measure the pressure in the wheel axle suspensions.
  • the load pressure sensor may be configured to measure the hydraulic pressure in the respective hydraulic wheel axle suspension arrangements of the tractor unit.
  • a certain ratio of the overall load of the working machine is provided on the wheel axle of the tractor unit.
  • the load on the wheel axle of the tractor unit will continuously be reduced until the wheel axle is not exposed to any load at all, at which moment the wheels of the tractor unit may be lifted off the ground.
  • the signal indicative of the unloading mode of operation of the working machine may be received from an operator controlled unloading actuating means, wherein the working machine is determined to be in the unloading mode of operation if the unloading actuating means is actuated.
  • the operator controlled unloading actuating means may be an actuation device positioned in the cabin of the tractor unit, such as on the instrument panel or in the vicinity of the gear shift lever or a tipping lever.
  • the operator controlled unloading actuating means may equally as well be arranged on any other positions of the working machine, such as on the trailer unit in the vicinity of the dump body or on the exterior surface of the cabin.
  • the operator controlled unloading actuating means may be the tipping lever of the working machine, such that when the operator of the vehicle actuates the tipping lever, i.e. order tipping of the dump body of the working machine, the working machine is determined to be in the unloading mode of operation.
  • the signal indicative of the unloading mode of operation of the working machine may be received from an inclination sensor arranged to measure an angle of inclination of a dump body connected to the frame unit, and the frame unit, relative to the longitudinal extension of the working machine, wherein the working machine is determined to be in the unloading mode of operation if the measured angle of inclination exceeds a predetermined angular threshold value.
  • an inclination sensor arranged to measure an angle of inclination of a dump body connected to the frame unit, and the frame unit, relative to the longitudinal extension of the working machine, wherein the working machine is determined to be in the unloading mode of operation if the measured angle of inclination exceeds a predetermined angular threshold value.
  • the working machine may comprise a tractor unit and a trailer unit comprising the frame unit, the tractor unit and the trailer unit being pivotally connected to each other by a joint arrangement allowing mutual rotation of the tractor unit and the trailer unit around a geometric axis having a horizontal component in the longitudinal direction of the working machine.
  • the example embodiment is applicable to vehicles having a geometrical pivot axis with a horizontal component, and preferably a major horizontal component, for allowing pivoting of the tractor unit and the trailer unit relative to each other.
  • the vertical component is often small or negligible, and thus the geometrical pivot axis can be considered to be substantially horizontal.
  • the wording "substantially horizontal” should be understood to include normal tolerances in regards to a horizontal axis. A deviation from an absolute horizontal axis by a few degrees, such as up to ten degrees should be considered to be within the scope of the wording of the present description. Also, the wording should be interpreted in view of a working machine standing still on a level surface. When the working machine is operated on a construction site, the horizontal axis is naturally not horizontal at all times as seen from a global coordinate system of the working machine. The presence of this "horizontal pivot axis" does however not exclude that there is also another geometrical pivot axis having a major vertical component, or a substantially vertical pivot axis, used for achieving an articulated vehicle or an articulated and frame-steered vehicle.
  • the wording "mutual rotation” should be understood to mean that the tractor unit is able to rotate relative to the trailer unit, and vice versa.
  • the front wheel axle and the rear wheel axle may be positioned on the trailer unit of the working machine.
  • the tipping point is, when applying the method of the present invention, positioned at a rear end of the working machine, which is beneficial since it is rather unlikely that the displacement of the center of gravity of the working machine, caused by the load in the dump body, will locate the center of gravity such that the tractor unit of the working machine will be lifted off the ground surface.
  • a control unit configured to control a working machine, the working machine comprising a front wheel axle and a rear wheel axle connected to a frame unit of the working machine at a distance from each other in a longitudinal direction of the working machine, the front wheel axle being connected to the frame unit by a front hydraulic wheel axle suspension arrangement and the rear wheel axle being connected to the frame unit by a rear hydraulic wheel axle suspension arrangement, wherein the control unit is configured to receive a signal indicative of an unloading mode of operation for the working machine; and fixate a distance in vertical direction between the front wheel axle and the frame unit in response to the received signal.
  • a computer program comprising program code means for performing any of the above described steps in relation to the first aspect of the present invention.
  • a computer readable medium carrying a computer program comprising program code means for performing any of the above described steps in relation to the first aspect of the present invention.
  • the working machine comprising a control unit as described above in relation to the second aspect of the present invention.
  • the working machine may comprise a tractor unit and a trailer unit comprising a frame unit, the tractor unit and the trailer unit being pivotally connected to each other by a joint arrangement allowing mutual rotation of the tractor unit and the trailer unit around a geometric axis having a horizontal component in the longitudinal direction of the working machine.
  • the working machine may further comprise a front wheel axle and a rear wheel axle connected to the frame unit at a distance from each other in a longitudinal direction of the working machine, the front wheel axle being connected to the frame unit by a front hydraulic wheel axle suspension arrangement and the rear wheel axle being connected to the frame unit by a rear hydraulic wheel axle suspension arrangement.
  • the front wheel axle and the rear wheel axle may be arranged at a rear end portion of the trailer unit.
  • Fig. 1 is a side view of a working machine in the form of a full suspension articulated hauler according to an example embodiment of the present invention
  • Fig. 2 is a perspective view illustrating in detail an example embodiment of the frame units and suspension arrangements of the articulated hauler in Fig. 1 ;
  • Figs. 3a - 3b are side views illustrating example embodiments of how to prevent the tractor unit to be lifted off the ground;
  • Fig. 4 is a flow chart of exemplifying method steps for executing a method according to an example embodiment of the present invention.
  • Fig. 1 is a side view of a working machine 1 in the form of a full suspension articulated hauler having a tractor unit 2 with a cab 3 for a driver and a trailer unit 4 with a platform having a dump body 5, here in the form of a container, arranged thereon, for receiving load.
  • the dump body 5 is preferably pivotally connected to the rear section and tiltable by means of a pair of tilting cylinders 6, for example hydraulic cylinders.
  • the tractor unit 2 has a frame unit 7, in the following also referred to as a front frame unit 7, and a pair of wheels 8 suspended from the front frame unit 7.
  • the trailer unit 4 has a frame unit 9, in the following also referred to as the rear frame unit 9, and two pair of wheels 10, 11 suspended from the rear frame unit 9.
  • the working machine is frame-steered, i.e. there is a joint arrangement 12 connecting the tractor unit 2 and the trailer unit 4 of the working machine 1.
  • the tractor unit 2 and the trailer unit 4 are pivotally connected to each other for pivoting around a substantially vertical pivot axis 13.
  • the working machine preferably comprises a hydraulic system having two hydraulic cylinders 14, steering cylinders, arranged on opposite sides of the working machine for turning the working machine by means of relative movement of the tractor unit 2 and the trailer unit 4.
  • the hydraulic cylinders can, however, be replaced by any other linear actuator for steering the machine, such as an electromechanical linear actuator.
  • the working machine further comprises a joint arrangement 15 connecting the tractor unit 2 and the trailer unit 4 of the working machine for allowing mutual rotation of the tractor unit 2 and the trailer unit 4 around a geometric axis (202 in Fig. 2) having a horizontal component in the longitudinal direction of the working machine 1.
  • each of the wheels comprises an individual hydraulic wheel axle suspension arrangement 204, 206 of which only the hydraulic wheel axle suspension arrangements on the trailer unit 4 is depicted in Fig. 1.
  • Fig. 2 illustrates the front frame unit 7 of the tractor unit 2, the rear frame unit 9 of the trailer unit 4, and the hydraulic wheel axle suspension arrangements 204, 206, 208 of the wheel axles 210, 212, 214.
  • the wheels 8, 10, 11 of the working machine 1 as well as the cabin 3 and the dump body 5 are excluded in Fig. 2.
  • the tractor unit 2 comprises the front frame unit 7 which is pivotally connected to the rear frame unit 9 of the trailer unit 4 at the joint
  • the tractor unit 2 may rotate around the geometric axis 202 at the joint arrangement 15 and rollover to the side of the cabin.
  • a hydraulic tractor wheel axle suspension arrangement 208 is connected to the front frame unit 7 of the tractor unit 2. More specifically, the hydraulic tractor wheel axle suspension arrangement 208 is arranged between the front frame unit 7 and a wheel axle 214 of the tractor unit 2. The hydraulic tractor wheel axle suspension arrangement 208 is positioned on each side of the front frame unit 7 such that each wheel 8 of the pair of wheels of the tractor unit 2 comprises an individual hydraulic tractor wheel axle suspension arrangement 208.
  • the trailer unit 4 comprises the rear frame unit 9.
  • the rear frame unit 9 is connected to a front wheel axle 212 and a rear wheel axle 210 which are arranged at a distance from each other in the longitudinal direction of the working machine 1. More specifically, the front wheel axle 212 and the rear wheel axle 210 are positioned in the vicinity of each other at a rear end of the rear frame unit 9.
  • the rear end of the rear frame unit 9 should be understood to mean that the front 212 and rear 210 wheel axles are positioned on the rear half of the rear frame unit 9 as seen in the longitudinal direction of the working machine.
  • the front wheel axle 212 of the trailer unit 4 comprises the above described pair of wheels 10 and the rear wheel axle 210 comprises the above described pair of wheels 11.
  • the front wheel axle 212 is connected to the rear frame unit 9 by a front hydraulic wheel axle suspension arrangement 204 and by a front wheel axle frame arrangement 216 which is pivotally connected to the rear frame unit 9 at a distance in front of the front wheel axle 212 as seen in the longitudinal direction of the working machine 1.
  • the front wheel axle 212 is connected to the rear frame unit 9 at each side of the rear frame unit 9, i.e. the front wheel axle 212 is connected to the rear frame unit 9 by means of a pair of front hydraulic wheel axle suspension arrangements 204.
  • the rear wheel axle 210 is connected to the rear frame unit 9 by a rear hydraulic wheel axle suspension arrangement 206 and by a rear wheel axle frame arrangement 218 which is pivotally connected to the rear frame unit 9 at a distance in front of the rear wheel axle 210 as seen in the longitudinal direction of the working machine 1.
  • the rear wheel axle 210 is connected to the rear frame unit 9 at each side of the rear frame unit 9, i.e. the rear wheel axle 210 is connected to the rear frame unit 9 by means of a pair of rear hydraulic wheel axle suspension arrangements 206.
  • the front wheel axle 212 thus comprises a front hydraulic wheel axle suspension arrangement 204 positioned at each side of the rear frame unit 9 and hence on each side of the front wheel axle 212.
  • the same applies for the rear wheel axle 210 namely that the rear wheel axle 210 comprises a rear hydraulic wheel axle suspension arrangement 206 positioned at each side of the rear frame unit 9 and hence on each side of the rear wheel axle 210.
  • each of the wheels 10, 11 on the front 212 and the rear 210 wheel axles is provided with an individual wheel suspension arrangement.
  • the front hydraulic wheel axle suspension arrangement 204 and the rear hydraulic wheel axle suspension arrangement 206 can hence be controlled individually.
  • the front hydraulic wheel axle suspension 204 can be compressed, expanded, or fixated relative to the rear frame unit 9 independently of the rear hydraulic wheel axle suspension arrangement 204. Also, the front hydraulic wheel axle suspension arrangement 204 on one side of the rear frame unit 9 can be individually controlled relative to the front hydraulic wheel axle suspension arrangement 204 positioned on the other side of the rear frame unit 9 as seen in the longitudinal direction of the working machine. The same applies for the rear hydraulic wheel axle suspension arrangement 206.
  • the rear frame unit 9 comprises a geometric axis 220, in the following referred to as the tipping axis 220 or tipping point.
  • the tipping axis 220 defines a position around which the working machine 1 can be unintentionally pivoted during unloading of the dump body 5.
  • the tipping axis 220 is a geometric axis positioned between the rear wheel axle 210 and the front wheel axle 212. During unloading of the working machine 1 , there is a risk that the center of gravity of the load in the dump body will be positioned rearward of the tipping axis 220, as seen in the longitudinal direction of the working machine, such that the wheels 8 of the tractor unit 2 may lift off the ground.
  • a signal may be received from a dump body tilting cylinder sensor which is arranged to detect actuation of the tilting cylinders 6.
  • the dump body tilting cylinder sensor is connected to the tilting cylinder 6.
  • the signal may also be provided from a load pressure sensor that detects the load on the wheel axle 214 of the tractor unit 2 and it is determined that the working machine 1 is in the unloading mode of operation if the load pressure is below, or falls below, a predetermined pressure threshold limit.
  • a load pressure sensor that detects the load on the wheel axle 214 of the tractor unit 2 and it is determined that the working machine 1 is in the unloading mode of operation if the load pressure is below, or falls below, a predetermined pressure threshold limit.
  • Fig. 3a when it is determined that the working machine 1 is in the unloading mode of operation, the distance between the rear wheel axle 210 and the rear frame unit 9 is fixated. In the illustrated embodiment depicted in Fig. 3a, the vertical distance between the front wheel axle 212 and the rear frame unit 9 has been reduced by compressing the front hydraulic wheel axle suspension
  • the distance in vertical direction between the rear wheel axle 210 and the rear frame unit 9 can be fixated by, for example, preventing hydraulic fluid from being drained from the rear hydraulic wheel axle suspension arrangement 206. More specifically, the hydraulic fluid may be prevented from being drained from the piston side of the rear hydraulic wheel axle suspension arrangement, when drainage of hydraulic fluid from the piston side compresses the rear hydraulic wheel axle suspension arrangement 206. Preventing hydraulic fluid from being drained from the hydraulic wheel axle suspension arrangement may be executed by controlling valves to be positioned in a closed state, wherein the valves are arranged downstream the hydraulic wheel axle suspension arrangement in fluid communication between the hydraulic wheel axle suspension arrangement and a hydraulic tank.
  • the hydraulic fluid may be hydraulic oil or any other suitable fluid for use in hydraulic cylinders.
  • Fig. 3b illustrating a further example embodiment of the present invention.
  • the difference between the example embodiment depicted in Fig. 3a and the example embodiment depicted in Fig. 3b is that in the embodiment illustrated in Fig. 3b, the vertical distance between the rear wheel axle 210 and the rear frame unit 9 is also reduced.
  • the front hydraulic wheel axle suspension arrangement 204 as well as the rear hydraulic wheel axle suspension arrangement 206 is each positioned at a maximum compression state thereof.
  • none of the hydraulic wheel axle suspension arrangements have a damping characteristic, i.e. the rear frame unit 9 can be considered to be rigidly connected to the ground surface.
  • the tipping axis 220 will be displaced rearward to the position on the rear frame unit 9 onto which the rear hydraulic wheel axle suspension arrangement 206 is fixated.
  • Positioning the hydraulic wheel axle suspension arrangement in a maximum compression state may be executed by, for example, compressing the respective hydraulic wheel axle suspension arrangements to such an amount that a portion of the rear wheel axle 210 and a portion of the front wheel axle 212 are in abutment with a portion of the rear frame unit 9, respectively.
  • the hydraulic wheel axle suspension arrangement may also be positioned in the maximum compression state when the piston of the hydraulic cylinders of the hydraulic wheel axle suspension arrangement is in the lower end position within the hydraulic cylinder.
  • positioning the hydraulic wheel axle suspension arrangements in the maximum compression state may be executed by controlling the above described valves to be positioned in an open state, such that hydraulic fluid is drained from the hydraulic wheel axle suspension arrangements to the hydraulic tank.
  • Fig. 4 illustrates a flow chart of exemplifying method steps for executing a method for reducing the risk of lifting the tractor unit 2 during unloading of the dump body 5 of the working machine.
  • a signal is received S1 that indicates that the working machine is in an unloading mode of operation.
  • the signal indicates that the working machine is about to start unloading the load in the dump body, or has already initiated unloading of the load in the dump body, which increases the risk of lifting the tractor unit 2.
  • the distance between the rear wheel axle 210 and the rear frame unit 9 is fixated S2. This can be accomplished by positioning the rear hydraulic wheel axle suspension arrangement in a lock-up mode for preventing a relative motion between the rear wheel axle 210 and the rear frame unit 9.
  • fixating the distance in vertical direction between the rear wheel axle 210 and the rear frame unit 9 can be accomplished by controlling S3 the flow of hydraulic fluid of the rear hydraulic wheel axle suspension arrangement 210.
  • hydraulic fluid can be prevented from being drained from the rear hydraulic wheel axle suspension arrangement.
  • fixating the distance in vertical direction between the rear wheel axle 210 and the rear frame unit 9 can be accomplished by compressing S4 the rear hydraulic wheel axle suspension arrangement 206 and the front hydraulic wheel axle suspension arrangement to a maximum compression state thereof, respectively. This can be executed by e.g. compressing the rear hydraulic wheel axle suspension arrangement and the front hydraulic wheel axle suspension arrangement to such an amount that a portion of the front wheel axle 212 and a portion of the rear wheel axle 210 is in abutment with a portion of the rear frame unit 9, respectively.

Abstract

The present invention relates to a method for controlling a working machine (1), said working machine comprising a front wheel axle (212) and a rear wheel axle (210) connected to a frame unit (9) of the working machine at a distance from each other in a longitudinal direction of the working machine, said front wheel axle (212) being connected to the frame unit (9) by a front hydraulic wheel axle suspension arrangement (204) and said rear wheel axle (210) being connected to the frame unit (9) by a rear hydraulic wheel axle suspension arrangement (206), characterized by comprising the steps of receiving (S1) a signal indicative of an unloading mode of operation for said working machine; and fixating (S2) a distance in vertical direction between the rear wheel axle (210) and the frame unit (9) in response to said received signal. The present invention also relates to a corresponding control unit and a working machine.

Description

A METHOD FOR CONTROLLING A WORKING MACHINE DURING
UNLOADING
TECHNICAL FIELD
The present invention relates to a method for controlling a working machine. The invention also relates to a control unit configured to control a working machine. The invention is applicable on vehicles, in particularly working machines such as articulated haulers. Although the invention will mainly be described in relation to an articulated hauler, it is also applicable for other vehicles having a dump body for loading and unloading of material.
BACKGROUND
In the field of heavy vehicles, working machines in the form of full suspension articulated vehicles are often used at construction sites or the like. A full suspension articulated vehicle comprises an individual suspension arrangement for each of the wheels of the working machine, thus providing efficient and comfortable suspension of the articulated vehicle. The articulated vehicle further comprises a tractor unit at which an operator cabin is provided, and a trailer unit provided with a dump body for loading material to be transported. The dump body is connected to a frame unit of the trailer unit and can be raised and lowered by tilting the dump body in relation to the frame unit, which most often is executed by using hydraulic tilting cylinders such that the material in the dump body can be unloaded to a position rearward of the articulated vehicle.
Furthermore, the tractor unit and the trailer unit of the articulated vehicle are often pivotally connected to each other by a joint arrangement allowing mutual rotation of the tractor unit and the trailer unit around a geometric axis having a horizontal component in the longitudinal direction of the articulated vehicle. Hereby, the articulated vehicle is able to manage the rough terrain that is often associated to construction sites.
However, during some especially unbeneficial situations when utilizing an articulated vehicle, such as e.g. during unloading of material from the dump body and the weight of the load in the dump body is too heavy and/or a large amount of material or a large and heavy stone gets stuck in the dump body, there is a risk that the center of gravity of the machine is displaced rearwards during the unloading operation such that the tractor unit will be raised above the ground. In these relatively extreme and rare situations, when the wheels of the tractor unit are thus raised above the ground such that no connection is present between the wheels and the ground, and since the tractor unit is pivotally connected to the trailer unit around a horizontal axis, the tractor unit may rotate and tip over such that the cabin may land on the ground.
There is thus a need to prevent that the working machine is lifted off the ground during unloading of the dump body. SUMMARY
It is an object of the present invention to provide a method which reduces the risk of lifting the working machine above the ground during unloading thereof compared to prior art solutions. The object is at least partly achieved by the method for controlling a working machine according to claim 1.
According to a first aspect of the present invention, there is provided a method for controlling a working machine, the working machine comprising a front wheel axle and a rear wheel axle connected to a frame unit of the working machine at a distance from each other in a longitudinal direction of the working machine, the front wheel axle being connected to the frame unit by a front hydraulic wheel axle suspension arrangement and the rear wheel axle being connected to the frame unit by a rear hydraulic wheel axle suspension arrangement, wherein the method comprises the steps of receiving a signal indicative of an unloading mode of operation for the working machine; and fixating a distance in vertical direction between the rear wheel axle and the frame unit in response to the received signal.
The wording "fixating a distance in the vertical direction" should in the following and throughout the entire description be interpreted as a fixation of the distance between the wheel axle and the frame unit. The distance is not needed to be vertical at all possible positions of the working machine as seen from a global coordinate system of the working machine. When, for example, the working machine is standing on a level ground surface, the distance between the wheel axle and the frame unit may be vertical, but if the working machine is standing in a slope, the distance between the wheel axle and the frame unit is vertical as seen from the inclination of the slope onto which the working machine is positioned. Also, there may be applications where the rear hydraulic wheel axle suspension arrangement is connected between the rear wheel axle and the frame unit with an inclination. Hence, the rear hydraulic wheel axle suspension arrangement is positioned with an inclination and is not fully vertical. In these situations, the distance between the front wheel axle and the frame unit should still be considered to be fixated in the vertical direction in response to the received signal.
Furthermore, it should be readily understood that the working machine comprises a hydraulic suspension arrangement on each side of the wheel axles, i.e. on each side of the frame as seen in the longitudinal direction of the working machine. Thus, the rear wheel axle comprises a hydraulic suspension arrangement on each side thereof, such that the wheels on each side of the rear wheel axle comprise an individual hydraulic suspension arrangement, thereby making the vehicle a full suspension working machine.
Also, in the case where the working machine comprises a tractor unit and a trailer unit as will be described further below, the front wheel axle should be interpreted as a front wheel axle of the trailer unit. Hence, the trailer unit comprises two wheel axles.
Still further, the signal indicative of an unloading mode of operation for the working machine should be interpreted as a signal indicating that the working machine is either intended to unload material from a dump body of the working machine, or is currently unloading the material with an indicated increased risk of lifting the working machine above the ground. Hence, the unloading mode may be an upcoming event or an already ongoing event. Details and examples of the unloading mode of operation are given below in relation to example embodiments of the present invention. Advantages of the invention are that when the rear wheel axle and the frame unit are fixated relative to each other, the tipping point, or tipping axis, of the working machine is moved from a position located at a position between the front wheel axle and the rear wheel axle, back to a position located approximately at the rear wheel axle as seen from a longitudinal direction of the working machine. More specifically, the tipping point is moved rearwards to the position where the wheels of the rear wheel axle are in contact with the ground surface. This is advantageous since the tipping point is moved rearwards of the working machine which means that there is a reduced risk that the total center of gravity of the working machine will be positioned rearwards of this tipping point, which thus reduces the risk of lifting the working machine above the ground during unloading thereof. The tipping point should be understood to mean a position of the working machine around which the working machine can be unintentionally pivoted during unloading thereof.
According to an example embodiment, the rear hydraulic wheel axle suspension arrangement may be positioned in a lock-up mode for preventing a relative motion between the rear wheel axle and the frame unit.
Hereby, the rear hydraulic wheel axle suspension arrangement provides no damping between the rear wheel axle and the frame unit which provides an un-elastic connection between the ground and the frame via the rear hydraulic wheel axle suspension arrangement. This un-elastic, non-damping, connection between the ground and the frame unit further secures that the tipping point is moved rearwards of the working machine. The lock-up mode may be provided in many different ways which will be described further below.
According to an example embodiment, the flow of hydraulic fluid of the rear hydraulic wheel axle suspension arrangement may be controlled. By controlling the flow of hydraulic fluid, hydraulic fluid may, for example, be prevented from being supplied to, or drained from, the rear hydraulic wheel axle suspension arrangement which will provide a "stiff connection between the rear wheel axle and the frame unit, i.e. the rear hydraulic wheel axle suspension arrangement has no damping characteristics. According to an example embodiment, hydraulic fluid may be prevented from being drained from the rear hydraulic wheel axle suspension arrangement. As described above, a "stiff connection" is provided between the rear wheel axle and the frame unit. Prevention of hydraulic fluid drainage may be accomplished by using valve arrangements positioned in fluid communication with the hydraulic wheel axle suspension arrangement. According to an example embodiment, the rear hydraulic wheel axle suspension arrangement and the front hydraulic wheel axle suspension arrangement may be compressed to a maximum compression state thereof, respectively.
The wording "maximum compression state" should be understood to mean a state of the hydraulic suspension arrangement where the suspension arrangement is compressed to an approximately maximum limit, at which no further compression is possible.
Hereby, the rear hydraulic wheel axle suspension arrangement does not have any damping characteristics and the tipping point will thus be moved rearwards of the working machine. Hence, it is further secured that the rear wheel axle carries load so that the tipping point is located at the rear wheel axle.
A further advantage is that both the front and the rear hydraulic wheel axle suspension arrangements can be compressed approximately simultaneously.
Hereby, the front and rear hydraulic wheel axle suspension arrangements can be controlled simultaneously without the need of separately controlling each of the suspension arrangements and still displacing the tipping point backwards.
Still further, another advantage is that the working machine does not have to rely on valves preventing hydraulic fluid from being drained from the rear hydraulic wheel axle suspension arrangement. Conversely, the present embodiment relies on the fact that hydraulic fluid should be drained from the rear hydraulic wheel axle suspension arrangement.
Positioning the rear hydraulic suspension arrangement in a maximum compression state may be executed by e.g. controlling the piston of the rear hydraulic wheel axle suspension arrangement to be positioned at an end position within a hydraulic cylinder thereof, or as according to another example embodiment, the rear hydraulic wheel axle suspension arrangement may be compressed such that a portion of the rear wheel axle and a portion of the frame unit are in abutment with each other. It should be readily understood that portions of the rear wheel axle and the frame unit may be portions which are connected to the respective rear wheel axle and the frame unit. For example, the portion of the rear wheel axle may be a bracket or the like which is connected to the rear wheel axle. Likewise, the portion of the frame unit may also be a bracket or the like which is connected to the frame unit. Other examples are of course also conceivable.
According to an example embodiment, the signal indicative of the unloading mode of operation of the working machine may be received from a dump body tilting cylinder sensor arranged to detect actuation of a tilting cylinder of a dump body connected to the frame unit, wherein the working machine is determined to be in the unloading mode of operation if the dump body tilting cylinder sensor detects that the tilting cylinder is actuated. Hereby, the dump body tilting cylinder sensor detects that unloading is initiated, i.e. the dump body is starting to rise for unloading the material located therein. The dump body tilting cylinder sensor may be positioned on the tilting cylinders for detecting when the tilting cylinders start to move. An advantage is that it is determined that unloading of the dump body is initiated relatively instantaneous from when the operator decides to unload the material.
According to an example embodiment, the working machine may further comprise a tractor unit and a trailer unit comprising the frame unit, wherein the signal indicative of the unloading mode of operation of the working machine may be received from a load pressure sensor arranged to measure the load pressure on a wheel axle of the tractor unit, wherein the working machine is determined to be in the unloading mode of operation if the measured load pressure on the wheel axle of the tractor unit is below a predetermined pressure threshold level. The load pressure sensor may be positioned on the wheel axle of the tractor unit. The load pressure sensor may be positioned in connection to the hydraulic wheel axle suspension arrangement of the wheel axle of the tractor unit to measure the pressure in the wheel axle suspensions. For example, the load pressure sensor may be configured to measure the hydraulic pressure in the respective hydraulic wheel axle suspension arrangements of the tractor unit. During normal operation of the working machine, or when the working machine is standing still without unloading the dump body, a certain ratio of the overall load of the working machine is provided on the wheel axle of the tractor unit. However, when the working machine is unloading material the load on the wheel axle of the tractor unit will continuously be reduced until the wheel axle is not exposed to any load at all, at which moment the wheels of the tractor unit may be lifted off the ground. An advantage is that the present invention can determine that the working machine is in the unloading mode of operation well before the load on the wheel axle of the tractor unit is reduced to such an amount that the tractor unit will be lifted off the ground.
According to an example embodiment, the signal indicative of the unloading mode of operation of the working machine may be received from an operator controlled unloading actuating means, wherein the working machine is determined to be in the unloading mode of operation if the unloading actuating means is actuated.
The operator controlled unloading actuating means may be an actuation device positioned in the cabin of the tractor unit, such as on the instrument panel or in the vicinity of the gear shift lever or a tipping lever. However, the operator controlled unloading actuating means may equally as well be arranged on any other positions of the working machine, such as on the trailer unit in the vicinity of the dump body or on the exterior surface of the cabin. According to an example, the operator controlled unloading actuating means may be the tipping lever of the working machine, such that when the operator of the vehicle actuates the tipping lever, i.e. order tipping of the dump body of the working machine, the working machine is determined to be in the unloading mode of operation.
According to an example embodiment, the signal indicative of the unloading mode of operation of the working machine may be received from an inclination sensor arranged to measure an angle of inclination of a dump body connected to the frame unit, and the frame unit, relative to the longitudinal extension of the working machine, wherein the working machine is determined to be in the unloading mode of operation if the measured angle of inclination exceeds a predetermined angular threshold value. Hereby, it is determined if the dump body is lifted and hence is initiating unloading thereof.
According to an example embodiment, the working machine may comprise a tractor unit and a trailer unit comprising the frame unit, the tractor unit and the trailer unit being pivotally connected to each other by a joint arrangement allowing mutual rotation of the tractor unit and the trailer unit around a geometric axis having a horizontal component in the longitudinal direction of the working machine. The example embodiment is applicable to vehicles having a geometrical pivot axis with a horizontal component, and preferably a major horizontal component, for allowing pivoting of the tractor unit and the trailer unit relative to each other.
Practically, the vertical component is often small or negligible, and thus the geometrical pivot axis can be considered to be substantially horizontal. The wording "substantially horizontal" should be understood to include normal tolerances in regards to a horizontal axis. A deviation from an absolute horizontal axis by a few degrees, such as up to ten degrees should be considered to be within the scope of the wording of the present description. Also, the wording should be interpreted in view of a working machine standing still on a level surface. When the working machine is operated on a construction site, the horizontal axis is naturally not horizontal at all times as seen from a global coordinate system of the working machine. The presence of this "horizontal pivot axis" does however not exclude that there is also another geometrical pivot axis having a major vertical component, or a substantially vertical pivot axis, used for achieving an articulated vehicle or an articulated and frame-steered vehicle.
Also, the wording "mutual rotation" should be understood to mean that the tractor unit is able to rotate relative to the trailer unit, and vice versa. According to an example embodiment, the front wheel axle and the rear wheel axle may be positioned on the trailer unit of the working machine.
Hereby, the tipping point is, when applying the method of the present invention, positioned at a rear end of the working machine, which is beneficial since it is rather unlikely that the displacement of the center of gravity of the working machine, caused by the load in the dump body, will locate the center of gravity such that the tractor unit of the working machine will be lifted off the ground surface.
According to a second aspect of the present invention, there is provided a control unit configured to control a working machine, the working machine comprising a front wheel axle and a rear wheel axle connected to a frame unit of the working machine at a distance from each other in a longitudinal direction of the working machine, the front wheel axle being connected to the frame unit by a front hydraulic wheel axle suspension arrangement and the rear wheel axle being connected to the frame unit by a rear hydraulic wheel axle suspension arrangement, wherein the control unit is configured to receive a signal indicative of an unloading mode of operation for the working machine; and fixate a distance in vertical direction between the front wheel axle and the frame unit in response to the received signal. Effects and features of the second aspect of the present invention are largely analogous to those described above in relation to the first aspect of the present invention.
According to a third aspect of the present invention, there is provided a computer program comprising program code means for performing any of the above described steps in relation to the first aspect of the present invention.
According to a fourth aspect of the present invention, there is provided a computer readable medium carrying a computer program comprising program code means for performing any of the above described steps in relation to the first aspect of the present invention.
Effects and features of the third and fourth aspects of the present invention are largely analogous to those described above in relation to the first aspect of the present invention.
According to a fifth aspect of the present invention, there is provided a working machine comprising a control unit as described above in relation to the second aspect of the present invention. According to an example embodiment, the working machine may comprise a tractor unit and a trailer unit comprising a frame unit, the tractor unit and the trailer unit being pivotally connected to each other by a joint arrangement allowing mutual rotation of the tractor unit and the trailer unit around a geometric axis having a horizontal component in the longitudinal direction of the working machine.
According to an example embodiment, the working machine may further comprise a front wheel axle and a rear wheel axle connected to the frame unit at a distance from each other in a longitudinal direction of the working machine, the front wheel axle being connected to the frame unit by a front hydraulic wheel axle suspension arrangement and the rear wheel axle being connected to the frame unit by a rear hydraulic wheel axle suspension arrangement.
According to an example embodiment, the front wheel axle and the rear wheel axle may be arranged at a rear end portion of the trailer unit.
Effects and features of the fifth aspect of the present invention are largely analogous to those described above in relation to the first aspect of the present invention. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of exemplary embodiments of the present invention, wherein:
Fig. 1 is a side view of a working machine in the form of a full suspension articulated hauler according to an example embodiment of the present invention;
Fig. 2 is a perspective view illustrating in detail an example embodiment of the frame units and suspension arrangements of the articulated hauler in Fig. 1 ; Figs. 3a - 3b are side views illustrating example embodiments of how to prevent the tractor unit to be lifted off the ground; and Fig. 4 is a flow chart of exemplifying method steps for executing a method according to an example embodiment of the present invention.
DETAIL DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness. Like reference character refer to like elements throughout the description.
Fig. 1 is a side view of a working machine 1 in the form of a full suspension articulated hauler having a tractor unit 2 with a cab 3 for a driver and a trailer unit 4 with a platform having a dump body 5, here in the form of a container, arranged thereon, for receiving load. The dump body 5 is preferably pivotally connected to the rear section and tiltable by means of a pair of tilting cylinders 6, for example hydraulic cylinders. The tractor unit 2 has a frame unit 7, in the following also referred to as a front frame unit 7, and a pair of wheels 8 suspended from the front frame unit 7. The trailer unit 4 has a frame unit 9, in the following also referred to as the rear frame unit 9, and two pair of wheels 10, 11 suspended from the rear frame unit 9.
The working machine is frame-steered, i.e. there is a joint arrangement 12 connecting the tractor unit 2 and the trailer unit 4 of the working machine 1. The tractor unit 2 and the trailer unit 4 are pivotally connected to each other for pivoting around a substantially vertical pivot axis 13.
The working machine preferably comprises a hydraulic system having two hydraulic cylinders 14, steering cylinders, arranged on opposite sides of the working machine for turning the working machine by means of relative movement of the tractor unit 2 and the trailer unit 4. The hydraulic cylinders can, however, be replaced by any other linear actuator for steering the machine, such as an electromechanical linear actuator.
The working machine further comprises a joint arrangement 15 connecting the tractor unit 2 and the trailer unit 4 of the working machine for allowing mutual rotation of the tractor unit 2 and the trailer unit 4 around a geometric axis (202 in Fig. 2) having a horizontal component in the longitudinal direction of the working machine 1.
Furthermore, the working machine 1 depicted in Fig. 1 is, as described above, a so- called full suspension articulated hauler. This means that each of the wheels comprises an individual hydraulic wheel axle suspension arrangement 204, 206 of which only the hydraulic wheel axle suspension arrangements on the trailer unit 4 is depicted in Fig. 1. A more detailed description of the hydraulic wheel axle
suspension arrangements is given below in relation to Fig. 2.
Reference is thus made to Fig. 2 which illustrates the front frame unit 7 of the tractor unit 2, the rear frame unit 9 of the trailer unit 4, and the hydraulic wheel axle suspension arrangements 204, 206, 208 of the wheel axles 210, 212, 214. For simplicity of depicting the frames, shafts and hydraulic wheel axle suspension arrangements, the wheels 8, 10, 11 of the working machine 1 , as well as the cabin 3 and the dump body 5 are excluded in Fig. 2.
As described above, the tractor unit 2 comprises the front frame unit 7 which is pivotally connected to the rear frame unit 9 of the trailer unit 4 at the joint
arrangement 15, thus allowing mutual rotation around the geometric axis 202 having a horizontal component in the longitudinal direction of the working machine 1. If the tractor unit 2 is lifted off the ground during e.g. unloading of the dump body 5, the tractor unit 2 may rotate around the geometric axis 202 at the joint arrangement 15 and rollover to the side of the cabin.
Furthermore, a hydraulic tractor wheel axle suspension arrangement 208 is connected to the front frame unit 7 of the tractor unit 2. More specifically, the hydraulic tractor wheel axle suspension arrangement 208 is arranged between the front frame unit 7 and a wheel axle 214 of the tractor unit 2. The hydraulic tractor wheel axle suspension arrangement 208 is positioned on each side of the front frame unit 7 such that each wheel 8 of the pair of wheels of the tractor unit 2 comprises an individual hydraulic tractor wheel axle suspension arrangement 208.
Moreover, the trailer unit 4 comprises the rear frame unit 9. The rear frame unit 9 is connected to a front wheel axle 212 and a rear wheel axle 210 which are arranged at a distance from each other in the longitudinal direction of the working machine 1. More specifically, the front wheel axle 212 and the rear wheel axle 210 are positioned in the vicinity of each other at a rear end of the rear frame unit 9. The rear end of the rear frame unit 9 should be understood to mean that the front 212 and rear 210 wheel axles are positioned on the rear half of the rear frame unit 9 as seen in the longitudinal direction of the working machine. The front wheel axle 212 of the trailer unit 4 comprises the above described pair of wheels 10 and the rear wheel axle 210 comprises the above described pair of wheels 11. The front wheel axle 212 is connected to the rear frame unit 9 by a front hydraulic wheel axle suspension arrangement 204 and by a front wheel axle frame arrangement 216 which is pivotally connected to the rear frame unit 9 at a distance in front of the front wheel axle 212 as seen in the longitudinal direction of the working machine 1. The front wheel axle 212 is connected to the rear frame unit 9 at each side of the rear frame unit 9, i.e. the front wheel axle 212 is connected to the rear frame unit 9 by means of a pair of front hydraulic wheel axle suspension arrangements 204. Likewise, the rear wheel axle 210 is connected to the rear frame unit 9 by a rear hydraulic wheel axle suspension arrangement 206 and by a rear wheel axle frame arrangement 218 which is pivotally connected to the rear frame unit 9 at a distance in front of the rear wheel axle 210 as seen in the longitudinal direction of the working machine 1. The rear wheel axle 210 is connected to the rear frame unit 9 at each side of the rear frame unit 9, i.e. the rear wheel axle 210 is connected to the rear frame unit 9 by means of a pair of rear hydraulic wheel axle suspension arrangements 206.
The front wheel axle 212 thus comprises a front hydraulic wheel axle suspension arrangement 204 positioned at each side of the rear frame unit 9 and hence on each side of the front wheel axle 212. The same applies for the rear wheel axle 210, namely that the rear wheel axle 210 comprises a rear hydraulic wheel axle suspension arrangement 206 positioned at each side of the rear frame unit 9 and hence on each side of the rear wheel axle 210. With the suspension arrangement as depicted in Fig. 2, each of the wheels 10, 11 on the front 212 and the rear 210 wheel axles is provided with an individual wheel suspension arrangement. The front hydraulic wheel axle suspension arrangement 204 and the rear hydraulic wheel axle suspension arrangement 206 can hence be controlled individually. More specifically, the front hydraulic wheel axle suspension 204 can be compressed, expanded, or fixated relative to the rear frame unit 9 independently of the rear hydraulic wheel axle suspension arrangement 204. Also, the front hydraulic wheel axle suspension arrangement 204 on one side of the rear frame unit 9 can be individually controlled relative to the front hydraulic wheel axle suspension arrangement 204 positioned on the other side of the rear frame unit 9 as seen in the longitudinal direction of the working machine. The same applies for the rear hydraulic wheel axle suspension arrangement 206.
Still further, the rear frame unit 9 comprises a geometric axis 220, in the following referred to as the tipping axis 220 or tipping point. The tipping axis 220 defines a position around which the working machine 1 can be unintentionally pivoted during unloading of the dump body 5. The tipping axis 220 is a geometric axis positioned between the rear wheel axle 210 and the front wheel axle 212. During unloading of the working machine 1 , there is a risk that the center of gravity of the load in the dump body will be positioned rearward of the tipping axis 220, as seen in the longitudinal direction of the working machine, such that the wheels 8 of the tractor unit 2 may lift off the ground.
Reference is now made to Figs. 3a and 3b which illustrate two example
embodiments of how to control the working machine 1 such that the risk of lifting the tractor unit 2 off the ground is reduced during an unloading mode of operation of the working machine. It is hence assumed that the working machine is determined to be in an unloading mode operation. The working machine 1 can be determined to be in the unloading mode of operation in a plurality of ways. For example, a signal may be received from a dump body tilting cylinder sensor which is arranged to detect actuation of the tilting cylinders 6. Hence, the dump body tilting cylinder sensor is connected to the tilting cylinder 6. The signal may also be provided from a load pressure sensor that detects the load on the wheel axle 214 of the tractor unit 2 and it is determined that the working machine 1 is in the unloading mode of operation if the load pressure is below, or falls below, a predetermined pressure threshold limit. Other alternatives are of course also conceivable. Turning first to Fig. 3a, when it is determined that the working machine 1 is in the unloading mode of operation, the distance between the rear wheel axle 210 and the rear frame unit 9 is fixated. In the illustrated embodiment depicted in Fig. 3a, the vertical distance between the front wheel axle 212 and the rear frame unit 9 has been reduced by compressing the front hydraulic wheel axle suspension
arrangement 204. Reducing the vertical distance between the front wheel axle 212 and the rear frame unit 9 is not necessary for the embodiment in Fig. 3a to function properly, but by doing so further secures that the rear wheel axle 210 is exposed to the load from the working machine 1. Hereby, by fixating the rear hydraulic wheel axle suspension arrangement, a "stiff connection is provided between the rear wheel axle 210 and the rear frame unit 9, i.e. the rear hydraulic wheel axle suspension arrangement 206 does not have any damping characteristics, which will displace the tipping point 220 rearwards to the position where the rear wheels 11 are in contact with the ground surface.
The distance in vertical direction between the rear wheel axle 210 and the rear frame unit 9 can be fixated by, for example, preventing hydraulic fluid from being drained from the rear hydraulic wheel axle suspension arrangement 206. More specifically, the hydraulic fluid may be prevented from being drained from the piston side of the rear hydraulic wheel axle suspension arrangement, when drainage of hydraulic fluid from the piston side compresses the rear hydraulic wheel axle suspension arrangement 206. Preventing hydraulic fluid from being drained from the hydraulic wheel axle suspension arrangement may be executed by controlling valves to be positioned in a closed state, wherein the valves are arranged downstream the hydraulic wheel axle suspension arrangement in fluid communication between the hydraulic wheel axle suspension arrangement and a hydraulic tank.
The hydraulic fluid may be hydraulic oil or any other suitable fluid for use in hydraulic cylinders.
Reference is now made to Fig. 3b illustrating a further example embodiment of the present invention. The difference between the example embodiment depicted in Fig. 3a and the example embodiment depicted in Fig. 3b is that in the embodiment illustrated in Fig. 3b, the vertical distance between the rear wheel axle 210 and the rear frame unit 9 is also reduced. In the embodiment of Fig. 3b, the front hydraulic wheel axle suspension arrangement 204 as well as the rear hydraulic wheel axle suspension arrangement 206 is each positioned at a maximum compression state thereof. Hereby, none of the hydraulic wheel axle suspension arrangements have a damping characteristic, i.e. the rear frame unit 9 can be considered to be rigidly connected to the ground surface. Hereby, the tipping axis 220 will be displaced rearward to the position on the rear frame unit 9 onto which the rear hydraulic wheel axle suspension arrangement 206 is fixated.
Positioning the hydraulic wheel axle suspension arrangement in a maximum compression state may be executed by, for example, compressing the respective hydraulic wheel axle suspension arrangements to such an amount that a portion of the rear wheel axle 210 and a portion of the front wheel axle 212 are in abutment with a portion of the rear frame unit 9, respectively. However, the hydraulic wheel axle suspension arrangement may also be positioned in the maximum compression state when the piston of the hydraulic cylinders of the hydraulic wheel axle suspension arrangement is in the lower end position within the hydraulic cylinder.
Furthermore, positioning the hydraulic wheel axle suspension arrangements in the maximum compression state may be executed by controlling the above described valves to be positioned in an open state, such that hydraulic fluid is drained from the hydraulic wheel axle suspension arrangements to the hydraulic tank.
In order to sum up, reference is made to Fig. 4 which illustrates a flow chart of exemplifying method steps for executing a method for reducing the risk of lifting the tractor unit 2 during unloading of the dump body 5 of the working machine. Firstly, a signal is received S1 that indicates that the working machine is in an unloading mode of operation. The signal indicates that the working machine is about to start unloading the load in the dump body, or has already initiated unloading of the load in the dump body, which increases the risk of lifting the tractor unit 2. In response to the received signal, the distance between the rear wheel axle 210 and the rear frame unit 9 is fixated S2. This can be accomplished by positioning the rear hydraulic wheel axle suspension arrangement in a lock-up mode for preventing a relative motion between the rear wheel axle 210 and the rear frame unit 9.
According to one example embodiment, fixating the distance in vertical direction between the rear wheel axle 210 and the rear frame unit 9 can be accomplished by controlling S3 the flow of hydraulic fluid of the rear hydraulic wheel axle suspension arrangement 210. For example, hydraulic fluid can be prevented from being drained from the rear hydraulic wheel axle suspension arrangement.
According to another example embodiment, fixating the distance in vertical direction between the rear wheel axle 210 and the rear frame unit 9 can be accomplished by compressing S4 the rear hydraulic wheel axle suspension arrangement 206 and the front hydraulic wheel axle suspension arrangement to a maximum compression state thereof, respectively. This can be executed by e.g. compressing the rear hydraulic wheel axle suspension arrangement and the front hydraulic wheel axle suspension arrangement to such an amount that a portion of the front wheel axle 212 and a portion of the rear wheel axle 210 is in abutment with a portion of the rear frame unit 9, respectively.
It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

Claims

1. A method for controlling a working machine (1), said working machine comprising a front wheel axle (212) and a rear wheel axle (210) connected to a frame unit (9) of the working machine at a distance from each other in a longitudinal direction of the working machine (1), said front wheel axle (212) being connected to the frame unit (9) by a front hydraulic wheel axle suspension arrangement (204) and said rear wheel axle (210) being connected to the frame unit (9) by a rear hydraulic wheel axle suspension arrangement (206), characterized by comprising the steps of:
- receiving (S1) a signal indicative of an unloading mode of operation for said working machine (1); and
- fixating (S2) a distance in vertical direction between the rear wheel axle (210) and the frame unit (9) in response to said received signal.
2. A method according to claim 1 , characterized by fixating said vertical distance by controlling (S3) the flow of hydraulic fluid to and/or from the rear hydraulic wheel axle suspension arrangement (206).
3. A method according to claim 2, characterized by preventing hydraulic fluid from being drained from the rear hydraulic wheel axle suspension arrangement (206).
4. A method according to claim 1 , characterized by compressing (S4) the rear hydraulic wheel axle suspension arrangement (206) and the front hydraulic wheel axle suspension arrangement (204) to a maximum compression state thereof, respectively.
5. A method according to claim 4, characterized by compressing the rear hydraulic wheel axle suspension arrangement (206) such that a portion of the rear wheel axle (210) and a portion of the frame unit (9) are in abutment with each other.
6. A method according to any one of the preceding claims, characterized by receiving the signal indicative of the unloading mode of operation of the working machine (1) from a dump body tilting cylinder sensor arranged to detect actuation of a tilting cylinder (6) of a dump body (5) connected to the frame unit (9), wherein the working machine (1) is determined to be in the unloading mode of operation if the dump body tilting cylinder sensor detects that the tilting cylinder (6) is actuated.
7. A method according to any one of the preceding claims, wherein the working machine (1) further comprises a tractor unit (2) and a trailer unit (4) comprising the frame unit (9), characterized by receiving the signal indicative of the unloading mode of operation of the working machine from a load pressure sensor arranged to measure the load pressure on a wheel axle (214) of the tractor unit (2), wherein the working machine (1) is determined to be in the unloading mode of operation if the measured load pressure on the wheel axle (214) of the tractor unit is below a predetermined pressure threshold level.
8. A method according to any one of the preceding claims, characterized by receiving the signal indicative of the unloading mode of operation of the working machine from an operator controlled unloading actuating means, wherein the working machine is determined to be in the unloading mode of operation if the unloading actuating means is actuated.
9. A method according to any one of the preceding claims, characterized by receiving the signal indicative of the unloading mode of operation of the working machine from an inclination sensor arranged to measure an angle of inclination of a dump body connected to the frame unit, and the frame unit, relative to the longitudinal extension of the working machine, wherein the working machine is determined to be in the unloading mode of operation if the measured angle of inclination exceeds a predetermined angular threshold value.
10. A method according to any one of the preceding claims, wherein said working machine (1) comprises a tractor unit (2) and a trailer unit (4) comprising said frame unit (9), said tractor unit (2) and said trailer unit (4) being pivotally connected to each other by a joint arrangement (15) allowing mutual rotation of the tractor unit (2) and the trailer unit (4) around a geometric axis (202) having a horizontal component in the longitudinal direction of the working machine (1).
11. A method according to claim 10, wherein said front wheel axle (212) and said rear wheel axle (210) are positioned on said trailer unit (4) of the working machine (1).
12. A method according to claims 10 or 11 , wherein said front wheel axle (212) and said rear wheel axle (210) are arranged at a rear end portion of the trailer unit.
13. A control unit configured to control a working machine (1), said working machine comprising a front wheel axle (212) and a rear wheel axle (210) connected to a frame unit (9) of the working machine at a distance from each other in a longitudinal direction of the working machine, said front wheel axle (212) being connected to the frame unit (9) by a front hydraulic wheel axle suspension arrangement (204) and said rear wheel axle (210) being connected to the frame unit (9) by a rear hydraulic wheel axle suspension arrangement (206), characterized in that the control unit is configured to:
- receive a signal indicative of an unloading mode of operation for said working machine; and
- control the rear hydraulic wheel axle suspension arrangement (206) so as to fixate a distance in vertical direction between the rear wheel axle (210) and the frame unit
(9) in response to said received signal.
14. A computer program comprising program code means for performing the steps of claims 1 - 12 when said program is run on a computer.
15. A computer readable medium carrying a computer program comprising program code means for performing the steps of any of claims 1 - 12 when said program is run on a computer.
16. A working machine comprising a control unit according to claim 13.
17. A working machine according to claim 16, comprising a tractor unit (2) and a trailer unit (4) comprising a frame unit (9), said tractor unit (2) and said trailer unit (4) being pivotally connected to each other by a joint arrangement (15) allowing mutual rotation of the tractor unit (2) and the trailer unit (4) around a geometric axis (202) having a horizontal component in the longitudinal direction of the working machine (1).
18. A working machine according to claim 17, further comprising a front wheel axle (212) and a rear wheel axle (210) connected to said frame unit (9) at a distance from each other in a longitudinal direction of the working machine, said front wheel axle (212) being connected to said frame unit (9) by a front hydraulic wheel axle suspension arrangement (204) and said rear wheel axle (210) being connected to said frame unit (9) by a rear hydraulic wheel axle suspension arrangement (206).
19. A working machine according to claims 17 or 18, wherein said front wheel axle (212) and said rear wheel axle (210) are arranged at a rear end portion of the trailer unit.
PCT/SE2014/000150 2014-12-17 2014-12-17 A method for controlling a working machine during unloading WO2016099340A1 (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2694730A1 (en) * 1992-08-17 1994-02-18 Michel Delcroix Safety device for semi-trailer vehicles with tipping bodies - has stabilising jacks between chassis frame and rear axle, controlled by extension of tipping jack, and tilt detector
US20050062239A1 (en) * 2003-09-19 2005-03-24 Case Llc Locking anti-motion suspension
EP2085299A2 (en) * 2008-02-01 2009-08-05 Deere & Company Articulated vehicle stabilization system
DE102009056239A1 (en) * 2009-12-02 2011-06-09 Daimler Ag Method for stabilizing a vehicle during a discharge process
US20140284120A1 (en) * 2011-12-27 2014-09-25 Aerospace Heavy Industry Equipment Co., Ltd. Dump truck

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2694730A1 (en) * 1992-08-17 1994-02-18 Michel Delcroix Safety device for semi-trailer vehicles with tipping bodies - has stabilising jacks between chassis frame and rear axle, controlled by extension of tipping jack, and tilt detector
US20050062239A1 (en) * 2003-09-19 2005-03-24 Case Llc Locking anti-motion suspension
EP2085299A2 (en) * 2008-02-01 2009-08-05 Deere & Company Articulated vehicle stabilization system
DE102009056239A1 (en) * 2009-12-02 2011-06-09 Daimler Ag Method for stabilizing a vehicle during a discharge process
US20140284120A1 (en) * 2011-12-27 2014-09-25 Aerospace Heavy Industry Equipment Co., Ltd. Dump truck

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