TRACTOR UNIT OF A WORKING MACHINE

TECHNICAL FIELD

The present invention relates to a method for preventing rollover of a tractor unit of a working machine. The invention also relates to a control unit configured to prevent rollover of a tractor unit of 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 type of articulated vehicles; such e.g. trucks having a joint arrangement connecting a tractor unit to a trailer unit thereof.

BACKGROUND

In the field of heavy vehicles, working machines in the form of articulated vehicles are often used at construction sites or the like. The articulated vehicle 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 and can be raised and lowered by tilting the dump body in relation to the frame unit, which most often is executed by use of 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 centre 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 the tractor unit is pivotally connected to the trailer unit around an horizontal axis, the tractor unit may rotate and tip over such that the cabin may land on the ground.

US 2014/0222299 describes an articulated vehicle which utilizes a visual, audible or tactile warning system that can be activated when the tractor unit is about to lift off the ground, to thereby warn the operator of the articulated vehicle of the situation. Although US 2014/0222299 describes a system that warns the operator of the upcoming situation, there is a need to prevent rollover of the trailer unit in the special cases where the tractor unit is lifted off the ground.

SUMMARY

It is an object of the present invention to provide a method that prevents that a tractor unit rolls over when it is lifted off the ground. The object is at least partly achieved by the method for preventing rollover of a tractor unit of a working machine according to claim 1. According to a first aspect of the present invention, there is provided a method for preventing rollover of a tractor unit of a working machine, the working machine comprising the tractor unit and a trailer unit 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, wherein the working machine comprises a longitudinal differential gearing arrangement interconnecting a tractor unit drive shaft of the tractor unit and a trailer unit drive shaft of the trailer unit; wherein the method comprises the steps of receiving a signal indicative of an upcoming rollover situation of the tractor unit of the working machine; and in response to the received signal, positioning the longitudinal differential gearing arrangement in a lock-up mode for preventing mutual rotation between the tractor unit drive shaft and the trailer unit drive shaft; rotatably fixating the tractor unit drive shaft to the tractor unit for preventing rotation of the tractor unit drive shaft and the tractor unit relative to each other; and rotatably fixating the trailer unit drive shaft to the trailer unit for preventing rotation of the trailer unit drive shaft and the trailer unit relative to each other. The invention 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.

Furthermore, the wording "mutual rotation" should be understood to mean that the tractor unit is able to rotate or pivot relative to the trailer unit, and vice versa.

Still further, the longitudinal differential gearing arrangement is an arrangement that, when being positioned in the lock-up mode, i.e. activated or engaged, transmits a torque from a longitudinally extending tractor unit drive shaft of the tractor unit to a longitudinally extending trailer unit drive shaft of the trailer unit, thus providing a 1 : 1 ratio between the drive shafts. Therefore, when positioning the longitudinal differential gearing arrangement in a lock-up mode, there is a 1 :1 rotation ratio between the tractor unit drive shaft and the trailer unit drive shaft. Hereby, the tractor unit drive shaft and the trailer unit drive shaft rotate with the same rotational speed and in the same rotational direction. Accordingly, if the tractor unit drive shaft is prevented from rotating, then also the trailer unit drive shaft is prevented from rotating, and vice versa.

Moreover, the signal indicative of an upcoming rollover situation is a signal that indicates that the working machine will be provided in a situation where there is a risk that the tractor unit will be lifted off the ground and rollover, i.e. flip over or fall on to the side thereof. The signal can be received from various sensors which are described below in relation to example embodiments of the present invention. It should be understood that the present invention is intended to function automatically which means that the method steps are executed, when receiving the above described signal, without active manoeuvring of a vehicle operator.

Finally, the wording "rotatably fixating" should be understood to mean that the tractor unit drive shaft is unable to rotate relative to the tractor unit, and vice versa, and the trailer unit drive shaft is unable to rotate relative to the trailer unit, and vice versa. Hence, the tractor unit drive shaft is connected to the tractor unit and the trailer unit drive shaft is connected to the trailer unit. Example embodiments of how to rotatably fixate the tractor unit drive shaft and the trailer unit drive shaft will be given below.

Advantages of the present invention are that the tractor unit is prevented to rotate relative to the trailer unit via the joint arrangement around the geometrical axis having the horizontal component in the longitudinal direction of the working machine. Hereby, in the case where the tractor unit will lift off the ground, the tractor unit and the trailer unit will function as a rigid unit which does not allow mutual rotation there between. The tractor unit will thus only be lifted off the ground keeping the tractor unit at the same rotational position relative to the trailer unit as it was before it was lifted. Also, already available functionalities of the working machine can be utilized without the need to provide e.g. a lock arrangement or the like to the joint arrangement for preventing the mutual rotation. According to an example embodiment, the tractor unit drive shaft and a tractor unit wheel axle of the tractor unit may be connected to each other, wherein the tractor unit drive shaft and the tractor unit wheel axle are rotatably fixated relative to each other. Hereby, the tractor unit drive shaft is prevented from rotating relative to the tractor unit wheel axle, which in turn makes the tractor unit drive shaft prevented from rotating relative to the tractor unit.

According to an example embodiment, the tractor unit drive shaft may be connected to a transverse differential gearing arrangement interconnecting a pair of wheels of the tractor unit wheel axle, wherein at least one wheel of the pair of wheels of the tractor unit wheel axle is provided with a brake; wherein the tractor unit drive shaft and the tractor unit wheel axle are rotatably fixated relative to each other by positioning the transverse differential gearing arrangement in a lock-up mode preventing mutual rotation between the pair of wheels of the tractor unit wheel axle; and braking the at least one wheel of the pair of wheels of the tractor unit wheel axle.

A transverse differential gearing arrangement is an arrangement that interconnects wheels of a wheel axle to each other such that they rotate in a 1 :1 ratio, which means that the wheels of the wheel axle rotate with the same speed and in the same rotational direction.

An advantage is that the wheels of the tractor unit wheel axle are prevented to rotate relative to each other. By also locking at least one of the wheels of the tractor unit prevents both of the wheels from rotating and the tractor unit drive shaft and the tractor unit wheel axle are thus rotatably fixated relative to each other.

According to an example embodiment, a pair of wheels of the tractor unit wheel axle may be provided with brakes, wherein the tractor unit drive shaft and the tractor unit wheel axle are rotatably fixated relative to each other by breaking the pair of wheels of the tractor unit wheel axle.

Hereby, the wheels of the tractor unit, and in turn thus also the wheel axle of the tractor unit, are rigidly connected to the tractor unit.

According to an example embodiment, the tractor unit drive shaft and the tractor unit may be rotatably fixated relative to each other by using a brake locking the tractor unit drive shaft and the frame of the tractor unit to each other. The tractor unit drive shaft is thus efficiently prevented from rotating relative to the tractor unit. The brake may, for example, be a parking brake of the working machine arranged between the tractor unit drive shaft and the frame. However, the brake may also be a service brake. According to an example embodiment, the tractor unit drive shaft may be connected to a drive unit arranged on the tractor unit, wherein the tractor unit drive shaft and the tractor unit are rotatably fixated relative to each other via a housing of the drive unit. Hereby, utilization of brakes or clutch arrangements of the drive unit can fixate the tractor unit drive shaft to the tractor unit.

According to an example embodiment, the trailer unit drive shaft and a trailer unit wheel axle of the trailer unit may be connected to each other, wherein the trailer unit drive shaft and the trailer unit wheel axle are rotatably fixated relative to each other.

Hereby, the trailer unit drive shaft is prevented to rotate relative to one of the wheel axles of the trailer unit. According to an example embodiment, the trailer unit drive shaft may be connected to a transverse differential gearing arrangement interconnecting a pair of wheels of the trailer unit wheel axle, wherein at least one wheel of the pair of wheels of the trailer unit wheel axle is provided with a brake, wherein the trailer unit drive shaft and the trailer unit wheel axle are rotatably fixated relative to each other by positioning the transverse differential gearing arrangement in a lock-up mode preventing mutual rotation between the pair of wheels of the trailer unit wheel axle; and braking the at least one wheel of the pair of wheels of the trailer unit wheel axle.

The transverse differential gearing arrangement connects the pair of wheels of the trailer unit wheel axle such that a 1 :1 ratio is provided between the wheels. Hereby, the wheels rotate with the same speed and in the same rotational direction in comparison to each other when the transverse differential gearing arrangement is positioned in the lock-up mode. Hereby, the wheels of the trailer unit wheel axle are prevented to rotate relative to each other and by locking at least one of the wheels of the trailer unit wheel axle will hence prevent both wheels from rotating. The trailer unit wheel axle will thus not be able to rotate which will also prevent the trailer unit drive shaft to rotate relative to the trailer unit wheel axle. According to an example embodiment, a pair of wheels of the trailer unit wheel axle may be provided with brakes, wherein the trailer unit drive shaft and the trailer unit wheel axle are rotatably fixated relative to each other by braking the pair of wheels of the trailer unit wheel axle.

By braking both of the wheels of the trailer unit wheel axle will efficiently prevent the trailer unit wheel axle from rotating. Hereby, the transverse differential gearing arrangement is not in need of being positioned in the lock-up mode for properly rotatably fixating the trailer unit drive shaft and the trailer unit wheel axle relative to each other.

According to an example embodiment, the trailer unit drive shaft and the trailer unit may be rotatably fixated relative to each other by using a brake locking the trailer unit drive shaft and the frame of the trailer unit to each other.

The brake may, for example, be a parking brake of the working machine positioned between the trailer unit drive shaft and the frame. The brake may however be a service brake of the working machine as well. According to an example embodiment, the trailer unit drive shaft and the trailer unit may be rotatably fixated via the trailer unit wheel axle being the foremost driven axle of the trailer unit.

In a case where the working machine comprises the option of six-wheel drive where the rearmost wheel axle is a driven wheel axle, the rearmost wheel axle of the trailer unit may also, or instead of the foremost driven axle, be rotatably fixated to the trailer unit.

According to an example embodiment, the signal indicative of an upcoming rollover situation may be received from a sensor determining that the working machine is in an unloading mode of operation.

Unloading is one of the modes where there is a risk that the tractor unit will be lifted off the ground and the tractor unit rolls over. According to an example embodiment, the signal indicative of an upcoming rollover situation may be received from a load pressure sensor arranged to measure the load pressure on a tractor unit wheel axle of the tractor unit, wherein the working machine is determined to be in the upcoming rollover situation if the measured load pressure on the tractor unit wheel axle is below a predetermined pressure threshold level.

The load pressure sensor is positioned on the tractor unit wheel axle. The load pressure sensor may be positioned in connection to the wheel axle suspension arrangement of the tractor unit wheel axle to measure the pressure in the wheel axle suspensions. For example, if the wheel axle suspension is a hydraulic wheel axle suspension, the load pressure sensor may be configured to measure the hydraulic pressure in the respective hydraulic wheel axle suspension arrangements. 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 tractor unit wheel axle. However, when the working machine is unloading material, the load on the tractor unit wheel axle will continuously be reduced until the tractor unit wheel axle is not exposed to any load at all, at which moment the wheels of the tractor unit will lift from the ground. An advantage is that it can be efficiently determined that the working machine is in the unloading mode of operation well before the load on the tractor unit wheel axle is reduced to such an amount that the tractor unit will lift off the ground.

According to an example embodiment, the signal indicative of an upcoming rollover situation may be received from an operator controlled unloading actuating means, wherein the working machine is determined to be in the upcoming rollover situation if the unloading actuating means is actuated.

The operator controlled 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 e.g. the gear shift lever. However, the operator controlled 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 embodiment, the signal indicative of an upcoming rollover situation may be received from an inclination sensor arranged to measure an angle of inclination of the frame of the trailer unit relative to the longitudinal extension of the working machine, wherein the working machine is determined to be in the upcoming rollover situation if the measured angle of inclination exceeds a predetermined angular threshold value.

This is advantageous in e.g. a situation where the working machine is unloading and the foremost end of the trailer unit is lifted relative to the rearmost end of the trailer unit. Hereby, the tractor unit will also be lifted and eventually to such extent that the pair of wheels of the tractor unit will be lifted off the ground. The inclination sensor can be configured to measure an angle of inclination before the unloading procedure is started as well as continuously measuring an angle of inclination during the unloading procedure. Hereby, the angle of inclination during the unloading procedure is compared to the angle of inclination before the unloading procedure is started. According to an example embodiment, the signal indicative of an upcoming rollover situation may be received from an angular sensor arranged to measure an angular displacement of the trailer unit and the tractor unit relative to each other around the geometrical axis of the working machine, wherein the working machine is determined to be in the upcoming rollover situation if the measured angular displacement exceeds a predetermined angular threshold value.

Hereby, the signal indicative of an upcoming rollover situation is received once the tractor unit is lifted off the ground and starting to rollover. According to an example embodiment, the signal indicative of an upcoming rollover situation may be received from a dump body tilting cylinder sensor arranged to detect actuation of a tilting cylinder of a dump body of the working machine, wherein the working machine is determined to be in the upcoming rollover situation 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, a dog clutch may be used for interconnecting the tractor unit drive shaft with the trailer unit drive shaft. As an alternative, a friction disc clutch may be used. This friction disc clutch may be either a wet friction disc clutch or a dry friction disc clutch.

According to an example embodiment, the dog clutch may be actuated using a spring and deactivated pneumatically using compressed air.

According to a second aspect of the present invention, there is provided a control unit configured to prevent rollover of a tractor unit of a working machine, the working machine comprising the tractor unit and a trailer unit pivotally connected to each other by a joint arrangement allowing mutual rotation of the tractor unit and the trailer unit around a geometrical axis having a horizontal component in the longitudinal direction of the working machine, wherein the working machine comprises a longitudinal differential gearing arrangement interconnecting a tractor unit drive shaft of the tractor unit and a trailer unit drive shaft of the trailer unit; wherein the control unit is configured to receive a signal indicative of an upcoming rollover situation of the tractor unit of the working machine; and in response to the received signal position the longitudinal differential gearing arrangement in a lock-up mode to prevent mutual rotation between the tractor unit drive shaft and the trailer unit drive shaft; rotatably fixate the tractor unit drive shaft to the tractor unit to prevent rotation of the tractor unit drive shaft and the tractor unit relative to each other; and rotatably fixate the trailer unit drive shaft to the trailer unit to prevent rotation of the trailer unit drive shaft and the trailer unit relative to each other.

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 when the program is run on a computer.

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 when the program is run on a computer.

According to a fifth aspect of the present invention, there is provided a working machine comprising a control unit according to the above description in relation to the second aspect of the present invention.

Effects and features of the third, fourth and fifth aspects of the present invention are largely analogous to those described 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 an articulated hauler according to an example embodiment of the present invention;

Fig. 2 is a side view of the working machine in Fig. 1 during a rollover situation of the tractor unit of the working machine according to an example embodiment of the present invention; Fig. 3 is a perspective view illustrating wheels and drive shafts according to the example embodiment of the working machine in Figs. 1 and 2;

Fig. 4 is perspective view illustrating in detail an example embodiment of the drive shafts, wheel axles and differential gearing arrangements of the working machine depicted in Figs. 1 and 2; and

Fig. 5 is a flow chart of various activities 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 an 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 7 and a pair of wheels 8 suspended from the frame 7. The trailer unit 4 has a frame 9 and two pair of wheels 10, 11 suspended from the frame 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 can further comprise a joint arrangement 15 (depicted in further detail in Fig. 3) connecting the tractor unit and the trailer unit of the working machine for allowing mutual rotation of the tractor unit and the trailer unit around a geometrical axis 302 (see Fig. 3) having a horizontal component in the longitudinal direction of the working machine.

During specific working situations, in the following referred to as rollover situations of the tractor unit, the pair of wheels 8 of the tractor unit 2 is lifted off the ground.

Reference is therefore made to Fig. 2, which illustrates a rollover situation of the tractor unit 2 of the working machine 1. In the specific scenario depicted in Fig. 2, the working machine 1 is unloading load from the dump body 5. More specifically, in a case where the load that is to be unloaded from the dump body 5 is in the form of e.g. a large and heavy stone, the centre of gravity of the working machine, including the load, may be moved rearwards to such an extent that the tractor unit 2 is lifted off the ground as illustrated in Fig. 2 when the dump body 5 is tilted.

As described above, the working machine comprises a joint arrangement 15 connecting the tractor unit 2 and the trailer unit 4 for allowing mutual rotation of the tractor unit 2 and the trailer unit 4 around the geometrical axis (302 in Fig. 3) extending in the longitudinal direction of the working machine. In the situation depicted in Fig. 2, the tractor unit 2 may, when the wheels 8 are lifted off the ground, therefore rollover such that e.g. the cabin 3 could land on the side causing damage to the working machine 1 as well as being dangerous for the operator. The tractor unit 2 will hence tip due to the joint arrangement 15 of the working machine. Although the rollover situation described above and depicted in relation to Fig. 2 is related to a situation where the working machine is unloading load from the dump body 5, other working situations may also cause the tractor unit 2 to rollover when the wheels 8 of the tractor unit 2 are lifted off the ground. The rollover situation may, for example, also occur if the working machine is reversing and the trailer unit 4 is driven down a relatively steep downhill slope, or if the trailer unit 4 is driven out from a slope such that the rearmost pair of wheels 11 is out of contact with the ground, etc. Accordingly, the rollover situation should be understood to mean any situation where there is a risk that the tractor unit 2, or more specifically the pair of wheels 8 of the tractor unit 2, is lifted off the ground.

Turning now to Fig. 3, which in further detail illustrates the frame 7 of the tractor unit 2, in the following also referred to as the front frame 7, and the frame 9 of the trailer unit 4, in the following also referred to as the rear frame 9. Moreover, and as described above, the front frame 7 and the rear frame 9 are connected to each other by means of the joint arrangement 15 allowing mutual rotation of the tractor unit 2 and the trailer unit 4 around the geometrical axis 302 extending in the longitudinal direction of the working machine. When the tractor unit 2 is lifted off the ground as depicted in Fig. 2, the tractor unit 2 thus rotates around the geometrical axis 302 by means of the joint arrangement 15.

The tractor unit 2 comprises a drive unit 304 for propelling the working machine 1. The drive unit 304 may include both the engine as well as the gearbox. The drive unit 304 is hence connected to the front frame 7 of the tractor unit 2. Also, the tractor unit 2 comprises a tractor unit drive shaft 306, which in the following detailed description will be referred to as the first tractor unit drive shaft 306, connected to the drive unit 304 and arranged to propel the pair of wheels 8 of the tractor unit. The pair of wheels 8 of the tractor unit 8 is connected to a tractor unit wheel axle 312. The first tractor unit drive shaft 306 is in the example embodiment depicted in Fig. 3 connected to the drive unit 304 and to a longitudinal differential gearing arrangement 308 which will be described further below in relation to Fig. 4. Also, as will be described and depicted in further detail in relation to Fig. 4, the tractor unit wheel axle 312 is connected to the longitudinal differential gearing arrangement 308 via a tractor unit drive shaft 402, which in the following detailed description will be referred to as the second tractor unit drive shaft 402.

The trailer unit 4 comprises a trailer unit drive shaft 310 arranged to propel the foremost pair of wheels 10 of the trailer unit 4. The trailer unit drive shaft 310 is connected to the first tractor unit drive shaft 306 via the longitudinal differential gearing arrangement 308. The foremost pair of wheels 10 of the trailer unit 4 is connected to a front trailer unit wheel axle 3 4 and the rearmost pair of wheels 1 of the trailer unit 4 is connected to a rear trailer unit wheel axle 316. Furthermore, the trailer unit drive shaft 310 may be arranged to propel the rearmost pair of wheels 11 of the trailer in cases where the working machine is utilizing six-wheel drive. The six- wheel drive can be selectively arranged by means of a longitudinal differential arrangement (410 in Fig. 4) positioned between the front trailer unit wheel axle 314 and the rear trailer unit wheel axle 316. However, the working machine may also be arranged to utilize six-wheel drive at all times, which means that no longitudinal differential arrangement is needed and the rearmost pair of wheels 11 is driven at all time.

To describe the shafts, axles and how they are interconnected in further detail, reference is made to Fig. 4. The wheels 8, 10, 11 of the working machine, as well as the front 7 and rear 9 frames, are not included in Fig. 4 for illustrating other components in a better way.

As described above, the tractor unit 2 comprises the drive unit 304 including both the engine, for example an internal combustion engine, and the gearbox. Moreover, the tractor unit 2 also comprises the above described first tractor unit drive shaft 306 positioned between the drive unit 304 and the longitudinal differential gearing arrangement 308. The longitudinal differential gearing arrangement 308 is further connected to the trailer unit drive shaft 310 of the trailer unit 4 as well as to the second tractor unit drive shaft 402 arranged between the longitudinal differential gearing arrangement 308 and a transverse differential gearing arrangement 404 of the tractor unit 2. The transverse differential gearing arrangement 404 is arranged to connect the pair of wheels 8 of the tractor unit to each other such that no mutual rotation between the wheels are allowed. Hence, when the transverse differential gearing arrangement 404 is actuated, i.e. positioned in a lock-up mode, the wheels 8 on the tractor unit wheel axle 312 rotate with a 1:1 ratio, i.e. they rotate with the same speed and in the same direction.

More specifically, when the longitudinal differential gearing arrangement 308 is positioned in a lock-up mode, i.e. when the longitudinal differential gearing arrangement 308 is actuated, the first tractor unit drive shaft 306 arranged between the drive unit 304 and the longitudinal differential gearing arrangement 308 is connected to the trailer unit drive shaft 310 such that no relative rotation is allowed between these shafts. Hence, the first tractor unit drive shaft 306 and the trailer unit drive shaft 310 rotates with a 1 :1 ratio, i.e. with the same speed and in the same rotational direction. Also, the second tractor unit drive shaft 402 arranged between the longitudinal differential gearing arrangement 308 and the transverse differential gearing arrangement 404 is connected to the trailer unit drive shaft 310 such that mutual rotation between these shafts is prevented. Accordingly, when the

longitudinal differential gearing arrangement 308 is positioned in the lock-up mode, the trailer unit drive shaft 310 and the second tractor unit drive shaft 402 arranged between the longitudinal differential gearing arrangement 308 and the transverse differential gearing arrangement 404 rotate with a 1 :1 ratio, i.e. the trailer unit drive shaft 310 and the second tractor unit drive shaft 402 rotate with the same speed and in the same rotational direction.

Furthermore, the above described joint arrangement 15 allowing mutual rotation of the tractor unit and the trailer unit about the geometrical axis is depicted with dashed lines in Fig. 3.

The trailer unit 4 comprises, as described above, the trailer unit drive shaft 310 which is connected to the longitudinal differential gearing arrangement 308. It should be readily understood that the trailer unit drive shaft 310 may be connected to the longitudinal differential gearing arrangement 308 via other shafts positioned there between. Furthermore, a brake 406 is arranged on the trailer unit drive shaft 310 which is arranged to lock the trailer unit drive shaft 310 to the frame 9 of the trailer unit 4. The brake 406 may for example be a parking brake. This parking brake may off course be positioned on the first tractor unit drive shaft 306 positioned between the drive unit 304 and the longitudinal differential gearing arrangement 308 as well, connecting the first tractor unit drive shaft 306 to the front frame 7 of the tractor unit 2. As a still further option, the parking brake may be positioned on the second tractor unit drive shaft 402 arranged between the longitudinal differential gearing

arrangement 308 and the transverse differential gearing arrangement 404, connecting the second tractor unit drive shaft 402 to the front frame 7 of the tractor unit 2. However, if the parking brake is positioned on one of the first 306 or second 402 tractor unit drive shafts instead of on the trailer unit drive shaft 310, the trailer unit drive shaft 310 needs to be fixated relative to the rear frame 9 by means of other arrangements. Moreover, the trailer unit drive shaft 310 is connected to a transverse differential gearing arrangement 408 which in turn is connected to the front trailer unit wheel axle 314. The transverse differential gearing arrangement 408 connected to the front trailer unit wheel axle 314, which in the following will be referred to as the trailer front transverse differential gearing arrangement, is configured to connect the pair of wheels 10 of the front trailer unit wheel axle 314 to each other. When the trailer front transverse differential gearing arrangement is arranged in a lock-up mode, i.e. when it is activated, the pair of wheels 10 of the front trailer unit wheel axle 314 is prevented from rotating relative to each other. Hence, the wheels 10 are configured to rotate in a 1 :1 ratio, i.e. the wheels 10 rotate with the same rotational speed and in the same direction.

The trailer unit drive shaft 310 is further connected to the above described longitudinal differential arrangement 410. When the longitudinal differential arrangement 410 is positioned in a lock-up mode, i.e. when it is engaged, the rear trailer unit wheel axle 316 is a driven axle and the working machine is hence operated in a six-wheel drive mode. Furthermore, the rear trailer unit wheel axle 316 is connected to a transverse differential gearing arrangement 318, in the following referred to as the trailer rear transverse differential gearing arrangement 412. The trailer rear transverse differential gearing arrangement 412 is arranged to connect the pair of wheels 11 of the rear trailer unit wheel axle 316 such that a 1:1 ratio is provided, such that the wheels 11 of the rear trailer unit wheel axle 316 rotate with the same rotational speed and in the same direction.

Still further, all the wheels 8, 10, 11 of the working machine 1 are provided with brakes, e.g. service brakes. Although these brakes are not illustrated in detail in any of the drawings, the skilled person should readily understand that these brakes are configured to brake their respective wheel in a normal fashion known in the art.

In order to prevent the tractor unit 2 to rollover when it is lifted off the ground, it is necessary to prevent the tractor unit 2 to rotate relative to the trailer unit 4 around the joint arrangement 15. This is achieved by rotatably fixating one of the first 306 and second 402 tractor unit drive shafts relative to the tractor unit 2, the trailer unit drive shaft 310 relative to the trailer unit 4, and preventing mutual rotation between the tractor unit drive shaft and the trailer unit drive shaft. By rotatably fixating one of the tractor unit drive shafts 306, 402 relative to the tractor unit 2 will prevent the tractor unit 2 to rotate around the tractor unit drive shaft 306, 402. Likewise, rotatably fixating the trailer unit drive shaft 310 relative to the trailer unit 4 will prevent the trailer unit 4 to rotate around the trailer unit drive shaft 3 0. Hereby, the drive shafts are rotatably fixated to the tractor unit 2 and the trailer unit 4, respectively. In order to prevent mutual rotation between the tractor unit drive shafts 306, 402 and the trailer unit drive shaft 310, the above described longitudinal differential gearing

arrangement 308 is positioned in the lock-up mode.

The following will now describe embodiments of the present invention for rotatably fixating the first 306 and the second 402 tractor unit drive shafts to the tractor unit and the trailer unit drive shaft 310 to the trailer unit 4, respectively. Reference is first made to the tractor unit 2 and example embodiments describing how to rotatably fixate the tractor unit drive shafts to the tractor unit.

According to an example embodiment, the second tractor unit drive shaft 402 can be rotatably fixated to the tractor unit 2 by rotatably fixating the second tractor unit drive shaft 402 and the tractor unit wheel axle 312 relative to each other. This can be accomplished by braking the pair of wheels 8 of the tractor unit wheel axle 312. Hereby, the tractor unit wheel axle 312 is fixated to the frame 7 of the tractor unit 2 via the brakes. By braking the wheels 8 it is not possible to rotate the tractor unit wheel axle 312, and thus not the tractor unit 2 (since the tractor unit wheel axle 312 is connected to the frame 7 of the tractor unit 2 via wheel axle suspensions), around the geometrical axis 302 without rotating the second tractor unit drive shaft 402, i.e. the second tractor unit drive shaft 402 and the tractor unit wheel axle 312 are not rotatable relative to each other.

The second tractor unit drive shaft 402 and the tractor unit wheel axle 312 may also be rotatably fixated relative to each other by braking one of the wheels 8 of the tractor unit wheel axle 312 and positioning the transverse differential gearing arrangement 404 of the tractor unit 2 in the lock-up mode. Hereby, one of the wheels 8 of the tractor unit wheel axle 312 is fixated to the frame 7 of the tractor unit 2 via the wheel brake and hence prevented from rotating, and since the transverse differential gearing arrangement 404 of the tractor unit 2 is positioned in the lock-up mode, the other wheel 8 of the tractor unit wheel axle 312 is hence also prevented from rotating, as mutual rotation is prevented. By braking one of the wheels and positioning the transverse differential gearing arrangement 404 in the lock-up mode, it is not possible to rotate the tractor unit wheel axle 312, and thus not the tractor unit 2 (since the tractor unit wheel axle 312 is connected to the frame 7 of the tractor unit 2 via wheel axle suspensions), around the geometrical axis 302 without rotating the second tractor unit drive shaft 402, i.e. the second tractor unit drive shaft 402 and the tractor unit wheel axle 312 are not rotatable relative to each other.

According to another example embodiment, the first tractor unit drive shaft 306 connected between the drive unit 304 and the longitudinal differential gearing arrangement 308 may be rotatably fixated to the tractor unit 2 by using a brake (not shown) locking the first tractor unit drive shaft 306 to the frame 7 of the tractor unit 2. The first tractor unit drive shaft 306 may however also be rotatably fixated to the tractor unit 2 by means of braking arrangement, or clutches, positioned in the drive unit, preferably positioned in the gearbox, which locks the first tractor unit drive shaft 306 to a housing of the drive unit 304, and in turn to the frame 7 of the tractor unit 2.

Turning now to the trailer unit 4, or more specifically to embodiments of how to rotatably fixating the trailer unit drive shaft 310 to the trailer unit 4. The embodiments first described assume that the longitudinal differential arrangement 410 of the trailer unit 4 is disengaged such that the rear trailer unit wheel axle 316 is a non-driven axle. Thereafter, example embodiments of how to rotatably fixating the trailer unit drive shaft 310 of the trailer unit 4 to the trailer unit 4 will be given for a six-wheel driven working machine, i.e. when the longitudinal differential arrangement 410 of the trailer unit 4 is engaged. When the working machine 1 is operated in a four-wheel driven mode, the trailer unit drive shaft 310 can be rotatably fixated to the trailer unit 4 by means of rotatably fixating the trailer unit drive shaft 310 to the front trailer unit wheel axle 314. This can be achieved by locking the brakes of the wheels 10 arranged on the front trailer unit wheel axle 314, i.e. the brakes of the wheels 10 positioned on the front trailer unit wheel axle 314 are actuated. Hereby, the front trailer unit wheel axle 314 is prevented to rotate since it is locked to the trailer unit 4. The trailer unit drive shaft 310 may also be rotatably fixated to the front trailer unit wheel axle 314 by means of braking only one of the wheels 10 and positioning the trailer front transverse differential gearing arrangement 408 in a lock-up mode. Hereby, one of the wheels 10 is prevented from rotating since the brake is actuated. At the same time the other wheel is also prevented from rotating since the trailer front transverse differential gearing arrangement 408 is positioned in the lock-up mode. By braking the wheels 10, or one of the wheels and positioning the trailer front transverse differential gearing arrangement in the lock-up mode, it is not possible to rotate the trailer unit drive shaft 3 0 relative to the front trailer unit wheel axle 314, and since the front trailer unit wheel axle 314 is connected to the frame 9 of the trailer unit 4 via wheel axle suspensions, the trailer unit 4 will prevent the trailer unit drive shaft 310 from rotating. When the working machine 1 is operated in a six-wheel driven mode, i.e. when the longitudinal differential arrangement 410 of the trailer unit 4 is engaged such that the rear trailer unit wheel axle 3 6 is a driven axle, the trailer unit drive shaft 310 can be rotatably fixated to the trailer unit 4 by means of rotatably fixating the trailer unit drive shaft 310 to the rear trailer unit wheel axle 316. This can be achieved by locking the brakes of the wheels 11 of the rear trailer unit wheel axle 316, i.e. both of the brakes of the wheels 11 positioned on the rear trailer unit wheel axle 316 are actuated. Hereby, the rear trailer unit wheel axle 316 is prevented from rotating since it is locked to the trailer unit 4. The trailer unit drive shaft 310 may also be rotatably fixated to the rear trailer unit wheel axle 316 by means of braking only one of the wheels 11 and positioning the trailer rear transverse differential gearing arrangement 412 in a lock-up mode. Hereby, one of the wheels 11 is prevented from rotating since the brake is actuated. At the same time the other wheel is also prevented from rotating since the trailer rear transverse differential gearing arrangement 412 is positioned in the lock-up mode. By braking the wheels 11 , or one of the wheels and positioning the trailer rear transverse differential gearing arrangement in the lock-up mode, it is not possible to rotate the trailer unit drive shaft 310 relative to the rear trailer unit wheel axle 316, and since the rear trailer unit wheel axle 316 is connected to the frame 9 of the trailer unit 4 via wheel axle suspensions, the trailer unit 4 will prevent the trailer unit drive shaft 310 from rotating. For both the four-wheel driven mode and the six-wheel driven mode, the trailer unit drive shaft 310 may be rotatably fixated to the trailer unit 4 by means of locking the trailer unit drive shaft 310 to the frame 9 of the trailer unit 4. This may be

accomplished by using the above described parking brake 406.

From the above description, the embodiments of rotatably fixating one of the first 306 and second 402 tractor unit drive shafts to the tractor unit may of course be combined with the embodiments of rotatably fixating the trailer unit drive shaft to the trailer unit, while at the same time positioning the longitudinal differential gearing arrangement 308 in the lock-up mode.

In order to sum up, reference is finally made to Fig. 5 which illustrates a flow chart of a method for preventing rollover of a working machine according to an example embodiment of the present invention. The following relates to the above described four-wheel driven mode. Also, it should be noted that the flow chart in Fig. 5 illustrates various activities that can be executed for the functioning of the present invention. Also, the method steps should be construed as executed at approximately the same time. Hence, after receiving the signal of an upcoming rollover situation, the longitudinal differential gearing arrangement is positioned in the lock-up mode, while at the same time rotatably fixating the tractor unit drive shaft to the tractor unit, as well as rotatably fixating the trailer unit drive shaft to the trailer unit.

Firstly, a signal is received S1 that indicates that the working machine 1 is determined to be in an upcoming rollover situation. More specifically, and as described above in relation to Fig. 2, the signal indicates that there is a risk that the wheels 8 of the tractor unit 2 of the working machine 1 will lift off the ground which could result in roll over of the tractor unit.

In response to the received signal of the upcoming rollover situation, the longitudinal differential gearing arrangement 308 is positioned S2 in a lock-up mode for preventing mutual rotation between the tractor unit drive shafts and the trailer unit drive shaft. Also, one of the tractor unit drive shafts is rotatably fixated S3 to the tractor unit 2 and the trailer unit drive shaft 310 is rotatably fixated S4 to the trailer unit 4. The step of rotatably fixating S3 one of the tractor unit drive shafts to the tractor unit may be accomplished by rotatably fixating S5 the second tractor unit drive shaft 402 to the tractor unit wheel axle 312. This may in turn be accomplished by positioning S6 the transverse differential gearing arrangement 404 of the tractor unit 2 in the lock-up mode and braking S7 the brake of one of the wheels 8 arranged on the tractor unit wheel axle. The step of rotatably fixating S5 the second tractor unit drive shaft 402 to the tractor unit wheel axle 312 relative to each other may also be accomplished by braking S8 the pair of wheels 8 on the tractor unit wheel axle 312, i.e. braking both of the wheels 8.

According to another example embodiment, the step of rotatably fixating S3 the first tractor unit drive shaft 306 to the tractor unit 2 may also be accomplished by locking S9 the first tractor unit drive shaft 306 to the frame 7 of the tractor unit 2. A parking brake may, for example, be used for locking the first tractor unit drive shaft 306 to the frame 7 of the tractor unit 2.

The step of rotatably fixating S4 the trailer unit driver shaft 3 0 to the trailer unit 4 may be accomplished by rotatably fixating S10 the trailer unit drive shaft 310 to the front trailer unit wheel axle 314. This may in turn be accomplished by positioning S11 the front trailer transverse differential gearing arrangement 408 in a lock-up mode and braking S12 the brake of one of the wheels 10 arranged on the front trailer unit wheel axle 314. The step of rotatably fixating S10 the trailer unit driver shaft 310 to the front trailer unit wheel axle 314 may also be accomplished by braking S13 the pair of wheels 10 of the front trailer unit wheel axle 314, i.e. braking both of the wheels 10 of the front trailer unit wheel axle 314.

According to another example embodiment, the step of rotatably fixating S4 the trailer unit drive shaft 310 to the trailer unit 4 may also be accomplished by locking S14 the trailer unit drive shaft 310 to the frame 9 of the trailer unit 4. A parking brake 406 may, for example, be used for locking the trailer unit drive shaft 310 to the frame 9 of the trailer unit 4.

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.