Method for determining whether or not ground contact loss is imminent for a wheel of a vehicle

A method is provided for determining whether or not ground contact loss is imminent for a wheel of a vehicle, the vehicle including a vehicle body having a vertical extension in a vertical direction, the wheel being allowed to be subjected to a relative vertical displacement, in the vertical direction, in relation to the vehicle body, the vehicle further being such that a maximum value of a vertical displacement of the wheel relative to the vehicle body is limited to a relative vertical displacement limit, the method including determining an actual relative vertical displacement of the wheel relative to the vehicle body, determining a limit margin as the difference between the actual relative vertical displacement and the relative vertical position limit, and determining that ground contact loss is imminent for a wheel if the limit margin is within a predetermined vertical threshold range.

BACKGROUND AND SUMMARY

The present disclosure relates to a method for determining whether or not ground contact loss is imminent for a wheel of a vehicle. Moreover, the present disclosure relates to a computer program, a computer readable medium, a control unit for a vehicle and/or a vehicle.

The present disclosure can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to an articulated hauler, the invention is not restricted to this particular vehicle, but may also be used in other vehicles, for instance other types of work machines such as a wheel loader, a dumper truck, or any other type of construction equipment.

A vehicle, for instance a work machine, generally comprises a plurality of wheels that are adapted to propel and/or brake the vehicle. In order to ensure that the operation of the vehicle is conducted in a desired manner, it may be desired to have information as regards the condition of one or more of the plurality of wheels.

For instance, it may be desired to receive information as regards whether or not ground contact loss is imminent for one or tore wheels of the vehicle. In the event that it is determined that ground contact loss is imminent, there is for instance a risk for wheel slip and a modification of the operation of the wheels may be desired.

For instance, in the event that the several wheels are driving a vehicle and it is determined that ground contact loss is imminent for one or more of the wheels, a driving torque may be distributed from the ground contact losing wheels to the wheels that are determined to maintain ground contact. Purely by way of example, the above transfer may be executed by means of one or more differentials.

As another example, in the event that the several wheels are braking a vehicle and it is determined that ground contact loss is imminent for one or more of the wheels, a braking torque may be redistributed from the around contact losing wheels to the wheels that are determined to maintain ground contact.

US 2007/0179699 A1 discloses a method for determining whether or not wheel slip is imminent for a vehicle wheel. The method proposed in US 2007/0179699 A1 detects the lateral acceleration of the vehicle, compares the lateral acceleration thus determined with a predetermined amount of lateral acceleration, and uses the result of that comparison for determining whether or not an electronic differential should be activated.

However, it would be desired to obtain more robust method for determining whether or not ground contact loss is imminent for a wheel.

It is desirable to provide a method for determining whether or not ground contact loss is imminent for a wheel of a vehicle, which method is straightforward to use.

As such, the present disclosure relates to a method for determining whether or not ground contact loss is imminent for a wheel of a vehicle. The vehicle comprises a vehicle body having a vertical extension in a vertical direction. The wheel is allowed to be subjected to a relative vertical displacement, in the vertical direction, in relation to the vehicle body. The vehicle further is such that a maximum value of a vertical displacement of the wheel relative to the vehicle body is limited to a relative vertical displacement limit.

The method comprises:

determining an actual relative vertical displacement of the wheel relative to the vehicle body,

determining a limit margin as the difference between the actual relative vertical displacement and the relative vertical position limit and

determining that ground contact loss is in imminent for a wheel if the limit margin is within a predetermined vertical threshold range.

The above discussed method implies that it is possible to determine whether or not ground contact loss is imminent for a wheel of a vehicle without having to analyze complex data, such as estimates of the speed or slip of the wheel and/or accelerations of the vehicle. Instead, the risk that contact loss is imminent may instead be determined on the basis of measure data that are simple to estimate and determine, e.g. an actual relative vertical displacement.

Optionally, the vehicle comprises a bogie system. The bogie system comprises a plurality of wheels and the bogie system is such that each one of the wheels is allowed to be subjected to a relative vertical displacement in relation to the vehicle body. Optionally, the bogie system comprises a bogie beam connecting the wheels. The bogie beam is pivotable in relation to the vehicle body. The method may comprise determining a pivot angle of the bogie beam in relation to the vehicle body and using the pivot angle as a value indicative of the actual relative vertical displacement.

Measuring the pivot angle is a straightforward way of determining the actual relative vertical displacement of one or more wheels arranged on a bogie beam.

A second aspect of the present disclosure relates to a method for controlling the operation of a wheel of a vehicle.

The method comprises:

determining whether or not ground contact loss is imminent for the wheel using the method according to the first aspect of the present disclosure,

determining that ground contact loss is imminent and

reducing the torque that is transmitted to the wheel.

A third aspect of the present disclosure relates to a computer program comprising program code means for performing the steps of any one of the methods of the first and/or second aspect of the present disclosure when the program is run on a computer.

A fourth aspect of the present disclosure relates to a computer readable medium carrying a computer program comprising program code means for performing the steps of any one of the methods of the first and/or second aspect of the present disclosure when the program product is run on a computer.

A fifth aspect of the present disclosure relates to a control unit for a vehicle. The control unit is adapted to determine whether or not ground contact loss is imminent for a wheel of the vehicle. The vehicle comprises a vehicle body having a vertical extension in a vertical direction. The wheel is allowed to be subjected to a relative vertical displacement, in the vertical direction, in relation to the vehicle body. The vehicle further is such that a maximum value of a vertical displacement of the wheel relative to the vehicle body Is limited to a relative vertical displacement limit.

The control unit is adapted to:

determine an actual relative vertical displacement of the wheel relative to the vehicle body,

determine a limit margin as the difference between the actual relative vertical displacement and the relative vertical position limit and

determine that ground contact loss is imminent for a wheel if the limit margin is within a predetermined vertical threshold range.

Optionally, the control unit is adapted to:

determine whether or not ground contact loss is imminent for the wheel using any one of the above discussed options,

determine that ground contact loss is imminent and

reduce the torque that is transmitted to the wheel.

A sixth aspect of the present disclosure relates to a vehicle, preferably a work machine, comprising a computer program according to the third aspect of the present disclosure and/or a computer readable medium according to the fourth aspect of the present disclosure and/or a control unit according to the fifth aspect of the present disclosure.

DETAILED DESCRIPTION

The invention will be described in the following for a vehicle in the form of an articulated hauler10such as the one illustrated inFIG. 1. The articulated hauler10should be seen as an example of a vehicle which could comprise a control unit according to the present invention and/or for which the method of the present invention may be used.

The vehicle10comprises a vehicle body12having a vertical extension in a vertical direction V. Moreover, and as is indicated inFIG. 1, the vehicle body12also has an extension in a longitudinal dimension L in the intended drive direction of the vehicle10.

TheFIG. 1vehicle10comprises a front vehicle portion14and a rear vehicle portion16. The front and rear vehicle portions14,6are connected to one another such that the front and rear vehicle portions can pivot relative to one another around a steering axis As extending substantially in the vertical dimension V and/or around a geometrical axis of rotation ARextending substantially along the longitudinal dimension L. Each one of the vehicle portions14,16forms part of the vehicle body12.

Moreover, the vehicle0comprises a plurality of wheels20,22,24each one of which is connected, directly or indirectly, to the vehicle body12. At least one of the wheels is allowed to be subjected to a relative vertical displacement, in the vertical direction V, in relation to the vehicle body12. Purely by way of example, one of the wheels20may be connected to the vehicle body by means of an individual suspension arrangement26. In theFIG. 1embodiment of the vehicle10, the individual suspension arrangement26is connected to the front vehicle portion1but in other embodiments, the rear vehicle portion16may instead, or also, comprise an individual suspension arrangement (not shown).

As another non-limiting example, the vehicle10may comprise a bogie system28. In theFIG. 1embodiment of the vehicle10, the bogie system28is connected to the rear vehicle portion16but in other embodiments, the front vehicle portion14may instead, or also, comprise a bogie system (not shown).

As may be gleaned fromFIG. 1, the bogie system28comprises a plurality of wheels22,24and the bogie system28is such that each one of the wheels22,24is allowed to be subjected to a relative vertical displacement in relation to the vehicle body12. To this end, the bogie system28may comprise a bogie beam30connecting the wheels22,24. The bogie beam30is pivotable around a pivot point32in relation to the vehicle body12. However, other implementations of a bogie system28need not comprise a beam. Purely by way of example, a bogie system may be a hydraulic bogie system (not shown).

FIG. 1further illustrates that the vehicle10comprises a control unit34. The control unit34may be adapted to determine whether or not ground contact loss is imminent for a wheel of the vehicle as will be described further hereinbelow.

The embodiment of the vehicle10illustrated inFIG. 1is such that a maximum value of a vertical displacement of a wheel20,22,24relative to the vehicle body2is limited to a relative vertical displacement limit.

For an individual suspension arrangement26, the above relative vertical displacement limit may for instance be defined by the maximum stroke of a hydraulic cylinder (not shown) of the individual suspension arrangement26. Instead of, or in addition to, a maximum stroke of a hydraulic cylinder, an individual suspension arrangement26may comprise a stop (not shown) which for instance may be attached to the vehicle body12and adapted to abut a portion of the individual suspension arrangement26to thereby limit the maximum value of a vertical displacement of the wheel20relative to the vehicle body12.

FIG. 2illustrates the bogie system28of theFIG. 1vehicle0. The bogie system28comprises a plurality of wheels22,24. TheFIG. 2implementation of the bogie system28comprises two wheels22,24that are located on the same side of the vehicle10. As such, each one of the two wheels22,24are located on the same side of a plane that extends along the longitudinal L and vertical V dimensions and which also coincides with the longitudinal centre line of the vehicle10. However, other implementations of the bogie system28may comprise wheels that are located on separate sides of the above discussed plane.

Irrespective of the position of the wheels22,24in relation of the vehicle10, the bogie system28is generally such that each one of the wheels22,24is allowed to be subjected to a relative vertical displacement in relation to the vehicle body12. Generally, a positive relative vertical displacement is a relative vertical displacement in a vertical direction away from the vehicle body12. Moreover, the bogie system28is generally such that a positive relative vertical displacement of one wheel22of the bogie system28results in a negative vertical displacement of another wheel24of the bogie system28.

Moreover,FIG. 2illustrates that the vehicle body12comprises a bogie beam stop34adapted to abut a portion of the bogie beam30to thereby obtain the relative vertical position limit. In fact,FIG. 2illustrates that the vehicle body12comprises two bogie beam stops34,36, one on each side of the pivot point32.

The vehicle10further generally comprises means for determining an actual relative vertical displacement of a wheel relative to the vehicle body12. For an individual suspension arrangement26, such a means may comprise a distance measuring arrangement (not shown), such as a sliding caliper (not shown) or the like, one end of which is connected to the vehicle body12and one end of which is connected to the wheel.

For a wheel of a bogie system28, the actual relative vertical displacement of a wheel relative to the vehicle body12may also be determined by a distance measuring arrangement. However, theFIG. 2implementation of the bogie system28comprises a pivot measuring arrangement38adapted to determine pivot angle a of the bogie beam30in relation to the vehicle body12. Using the pivot angle a and the distance from the pivot point32to the wheel22,24, the actual relative vertical displacement dvof a wheel relative to the vehicle body12may be determined using trigonometry. As such, the pivot angle a may be used as a value indicative of the actual relative vertical displacement.

Further, the value of the pivot angle a of the bogie beam30in relation to the vehicle body12when the bogie beam30abuts either one of the bogie beam stops34,36may be predetermined and stored in the control unit34for instance.

Instead of, or in addition to, the above discussed pivot measuring arrangement38, a vehicle10may comprise a sensor40, for instance an inductive sensor, wherein a first sensor portion42of the sensor40is connected to the bogie beam30and a second sensor portion44of the sensor40is connected to the stop34. Using the above two sensor portions42,44, it is possible to determine the vertical distance between the bogie beam30and the stop34,

FIG. 3is a rear view in perspective of a portion of theFIG. 2vehicle0illustrating the bogie beam30and the stops34,36.

FIG. 4illustrates a portion of the front wheel22of theFIG. 2andFIG. 3bogie system28. InFIG. 4, the dashed an dotted line illustrates the wheel22in its original position, the dotted line illustrates the wheel22in its end position, i.e. when it has reached its relative vertical position limit vl. Moreover, the solid line inFIG. 4illustrates the wheel22in an actual position, i.e. when the wheel has been subjected to an actual relative vertical displacement dv. A vertical direction away from the vehicle body, i.e. generally a vertical direction from the vehicle towards the ground, may be defined as a positive actual relative vertical displacement dv.

When the wheel22is in the position indicated inFIG. 4, the wheel22is in a location with a limit margin lmwhich is the difference between the actual relative vertical displacement dvand the relative vertical position limit V].

It should be noted that the front wheel22bogie system28is only used as an example hereinabove for presenting the measures: actual relative vertical displacement dv, relative vertical position limit ¼ and limit margin lmand that these measures may be determined for each one of the other wheels in a similar manner.

As has been intimated above, an aspect of the present invention relates to a method for determining whether or not ground contact loss is imminent for a wheel20,22,24of a vehicle10. The method may preferably be carried out by the control unit34. A flow chart illustrating the method is presented inFIG. 5and features of the method are presented hereinbelow.

A first step S1of the method comprises determining an actual relative vertical displacement dvof the wheel22,24,26relative to the vehicle body12. As has been advertised of hereinabove, the actual relative vertical displacement dvof the wheel22,24,26may be determined in a plurality of ways, such as a distance measuring arrangement, a pivot measuring arrangement and/or a sensor such as an inductive sensor. The measure actual relative vertical displacement dvis indicated for wheel22inFIG. 4.FIG. 4also indicates the relative vertical position limit V| for wheel24.

A second step S2of the method comprises determining a limit margin lmas the difference between the actual relative vertical displacement dv, which has been determined in the first step S1, and the relative vertical position limit vl.

A third step S3of the method comprises determining that ground contact loss is imminent for a wheel if the limit margin is within a predetermined vertical threshold range vl. Purely by way of example, the predetermined vertical threshold range vt, may be defined as 90% to 100% of the relative vertical position limit V|. Here, it should be noted that 0% indicates no vertical displacement and 100% indicates that the relative vertical position limit V| has been reached.

It is also envisage that the predetermined vertical threshold range vlmay be dependent on the configuration and/or operation of the vehicle10. Purely by way of example, one possibility may be that the vertical threshold range vlmay be relatively large for a vehicle10with six wheels that is in a condition wherein it is driven by four wheels (a so called 6×4 configuration). If it is determined that ground contact loss is imminent for one of the four wheels that are currently driving the vehicle10in a 6×4 configuration, two additional wheels may be operated to drive the vehicle10such that the vehicle assumes a so called 6×6 configuration. A reason for why the vertical threshold range vlmay be relatively large for the above scenario is that the propulsion of the vehicle is generally not impaired when switching from a 6×4 configuration to a 6×6 configuration.

As another non-limiting example, the vertical threshold range vlmay be relatively small for a vehicle10that is in a condition wherein it is driven by six wheels (a so called 6×6 configuration). If it is determined that ground contact loss is imminent for one of the six wheels that are currently driving the vehicle10in a 6×6 configuration, the propulsion of one or more wheels may have to be reduced or even removed and this may have a negative effect on e.g. the steering of the vehicle10.

It is also envisaged that the value of the vertical threshold range vlmay be dependent on at least one of the following parameters: the vehicle speed, the steering angle of the vehicle and the ground conditions. Instead of, or in addition to any one of the above parameters, the vertical threshold range vlmay be dependent on the velocity and/or acceleration of the actual relative vertical displacement dvof the wheel22,24.

In the event that the above method is implemented for a wheel that forms part of a bogie system28, the method may comprise determining which one of the wheels22,24of the bogie system28that has the largest positive relative vertical displacement.

The information that ground contact loss is imminent for a wheel may be used in a plurality of ways. Purely by way of example, the control unit34may be adapted to issue a signal that indicates that ground contact loss is imminent and optionally also for which wheel ground contact loss is imminent. As a non-limiting example, such a signal may be received by a driver information unit (not shown) which for instance may sound an alarm or present the information on a display (not shown).

FIG. 6illustrates a top view of theFIG. 1vehicle10. As may be gleaned fromFIG. 6, the vehicle10comprises a plurality of wheels20A,20B,22A,22B,24A,24B that are connected to a power source46, e.g. an internal combustion engine and/or an electric motor, via a transmission assembly48, drive shafts50,52and a plurality of differentials54,56,58,66, viz three transversal differentials54,56,58connecting a drive shaft50,52to wheel axles, a rear longitudinal differential66connecting two portions of a drive shaft50and a central longitudinal differential68connecting the drive shafts50,52.

The vehicle further comprises a plurality of brakes60A,60B,62A,62B,64A,64B for braking each one of the wheels20A,20B,22A,22B,24A,24B. However, it should be noted that other embodiments of the vehicle10may comprise one or more brakes (not shown) that is adapted to brake one or more wheels20A,20B,22A,22B,24A,24B.

The information whether or not ground contact loss is imminent for a wheel20,22,24of a vehicle0may be used in a method for controlling the operation of at least that wheel20,22,24vehicle10. Based on whether or not it is determined that ground contact loss is imminent for a wheel, the operation of the wheel may be modified. For instance, the level of the torque that is transmitted to a wheel for which ground contact loss is imminent, e.g. a brake torque or a propulsion torque, may have to be adjusted, generally reduced.

As such, a method for controlling the operation of a wheel of a vehicle may comprise the features that are presented hereinbelow.

The wheel operation control method may comprise determining whether or not ground contact loss is imminent for the wheel using the above discussed method. In the event that it is determined that ground contact loss is imminent the torque that is transmitted to the wheel is reduced.

For instance, if a brake force is applied to one of the wheels20A,20B,22A,22B,24A,24B of theFIG. 6vehicle10, which brake force results in a brake torque, and it is determined that ground contact loss is imminent for that wheel, the brake torque may be reduced for that wheel. Optionally, the brake torque may instead be increased for one or more of the wheels for which ground contact loss is not imminent in order to obtain an appropriate total brake force for the vehicle0. The above transfer of brake torque may be achieved by actuating one or more of the brakes60A,60B,62A,62B,64A,64B that have been discussed hereinabove with reference toFIG. 6,

In a similar vein, if a driving torque is applied to one of the wheels20A,20B,22A,22B,24A,24B of theFIG. 6vehicle10, and it is determined that ground contact loss is imminent for that wheel, the driving torque may be reduced for that wheel. Optionally, the driving torque may instead be increased for one or more of the wheels for which ground contact loss is not imminent in order to obtain an appropriate propulsion of the vehicle10.

The above transfer of brake torque may be achieved by actuating one or more, of the differentials54,56,58,66,68that have been discussed hereinabove with reference toFIG. 6.

Purely by way of example, at least one of the differentials54,56,58,66,68may comprise a differential arrangement (not shown) for selectively disengaging or locking, respectively, the differential54,56,58,66,68. As a non-limiting example, the differential arrangement may be adapted to assume a disengaging condition or a locking condition, respectively, in an on-off manner. In such an implementation of the differential arrangement, the differential arrangement may preferably comprise a lock (not shown). Optionally, the differential arrangement may be adapted to assume a disengaging condition or a locking condition, respectively, in a step-wise and/or continuous manner. In such an implementation of the differential arrangement, the differential arrangement may preferably comprise a clutch (not shown). It is also envisaged that an implementation of a differential arrangement may comprise a lock as well as a clutch.

The differential arrangement of a transversal differential may for instance be adapted to assume a disengaging condition or locking condition, respectively, individually for each one of the wheels that is associated with the transversal differential54,56,58. Optionally, the differential arrangement may be adapted to assume a disengaging condition or locking condition, respectively, for all the wheels that are associated with the transversal differential54,56,58.

If a driving torque is applied to one of the wheels20A,20B,22A,22B,24A,24B of a vehicle10comprising differentials54,56,58,66,68as have been discussed hereinabove, and it is determined that ground contact loss is imminent for that wheel, the driving torque may be reduced for that wheel, or for all the wheels that are connected to the same differential, by disengaging, fully or partially, the differential54,56,58,66,68associated with that wheel. Moreover, the differential for another wheel, or another set of wheels, may be operated so as to increase the torque distribution from the associated drive shaft to those wheels.

The above procedure will be exemplified hereinbelow in a situation in which it is determined that ground contact loss is imminent for the rearmost wheels24A,24B of theFIG. 6vehicle10. The rear transversal differential58may then be operated to disengage, partially or fully, the rearmost wheels24A,24B from the rear drive shaft50in order to reduce or cancel the torque distribution from the rear drive shaft50to the rearmost wheels24A,24B. Moreover, the transversal differential56associated with the front wheels22A,22B of the rear vehicle portion may be operated to lock, partially or fully, the front wheels22A,22B of the rear vehicle portion16to the rear drive shaft50in order to increase the torque distribution from the rear drive shaft50to the front wheels22A,22B of the rear vehicle portion16.

By using the above procedure, the risk that the rearmost wheels24A,24B will slip may be reduced due to the reduced or cancelled torque distribution to the rearmost wheels24A,24B. Moreover, by virtue of the fact that the torque distribution to the front wheels22A,22B of the rear vehicle portion16is increased, an appropriate propulsion of the vehicle10is nevertheless obtained.

Instead of, or in addition to, using the transversal differentials54,56,58for redistributing the torque between the wheels, the torque redistribution may be achieved by using the rear longitudinal differential66. As such, in the above-discussed scenario wherein it is determined that ground contact loss is imminent for the rearmost wheels24A,24B of theFIG. 6vehicle10, the rear longitudinal differential66may be operated so as to disengage, partially or fully, the rearmost portion of the drive shaft50from the foremost portion of the drive shaft50to thereby reduce the amount of torque that is distributed to the rearmost wheels24A,24B. To this end, though purely by way of example, the rear longitudinal differentia]66may comprise a clutch, such as a dog clutch. At the same time, the central longitudinal differential68may be operated so as to increase the torque distribution to the aft drive shaft50to thereby increase the torque distributed to the front wheels22A,22B of the rear vehicle portion16.