OA21246A - Auxiliary trailer. - Google Patents

Abstract

An auxiliary trailer is disclosed having a front body section and a rear body section. The front body section has a coupler arranged to be hitched to a hitch of a main vehicle, with the connection of the coupler and hitch inhibiting vertical movement of the front body relative to the main vehicle. The rear body section has at least one axle, and is articulatedly connected to the front body section about a hinge connection with a pivot axis substantially parallel to the axle(s). Either or both of the front and rear body sections includes at least one linear actuator arranged to exert a variable force on the other of the front or rear body sections to thereby induce a variable torque about the pivot axis. This urges the axle(s) toward a ground surface. A force vector of the variable pushing force is offset from the at least one axle.

Description

AUXILIARY TRAILER

CROSS-REFERENCE TO RELATED APPLICATIONS

This application daims priority from South African patent application number 2020/04587 filed on 24 July 2020, which is incorporated by reference herein.

FIELD OF THE INVENTION

The invention disclosed herein relates to road freight vehicles, and accessories therefor. It may find particular application in apparatuses and methods for distributing axle loads on freight vehicles.

BACKGROUND TO THE INVENTION

In the interest of maintaining the integrity of infrastructure and public safety, public roads are governed by régulations that include spécifications on the maximum allowable axle loads for road freight vehicles.

Third party freight carriers and manufacturers alike are incentivised to maximise payload weights per freight vehicle in order maximise profits. However, in order to comply with régulations that govern maximum axle loads, a freight vehicle requires a sufficient number of axles to distribute the weight of the freight across the axles, thereby bringing the per-axle load within regulatory limits.

However, road régulations also regulate the maximum number of axles in the axle unit of a freight vehicle, for example a semi-trailer. If the regulatory upper limits on the number of axles are exceeded, spécial or abnormal permits are required in order to legally use the vehicle on a public road. This may be a costly process and présents an additional operational burden on the transporter.

The Applicant considers there to be scope for improvement.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the présent invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided an auxiliary trader comprising: a front body section having a coupler arranged to be hitched to a hitch of a main vehicle, with the connection of the coupler and hitch inhibiting vertical movement of the front body relative to the main vehicle, and a rear body section with at least one axle and thaï is articulatedly connected to the front body section about a hinge connection, the hinge connection having a pivot axis substantially parallel to the at least one axle, wherein either or both of the front and rear body sections includes at least one linear actuator arranged to exert a variable force on the other of the front or rear body sections to thereby induce a variable torque about the pivot axis that in turn exerts a variable force on the at least one axle that urges the at least one axle toward a ground surface and transfers a portion of the weight of the main vehicle onto the at least one axle of the auxiliary trader, and wherein a force vector of the variable force is offset from the at least one axle.

These features may enable the auxiliary trader to be hitched to the main vehicle and a variable torque applied about the pivot axis of the auxiliary trader through the operation of the at least one linear actuator. A résultant variable force is exerted on the axle of the auxiliary trader (and a corresponding reaction force on coupler, hitch and main vehicle châssis), thereby causing some of the load on axles of the main vehicle to shift onto the axle of the auxiliary trader. This, in turn, may distribute the total weight of the payload over the additional axle (or axles) of the auxiliary trader, lowering the per-axle load of the vehicle as a whole.

The feature of the auxiliary trader being arranged to be hitched to (and thus unhitched from) the main vehicle enables the auxiliary trader to be easily unhitched, should the payload weight of the main vehicle be such that the additional axle or axles of the auxiliary trader are not required.

Further features provide for the hitch and coupler connection to be articulated so as to enable horizontal movement of the front body section relative to the main vehicle while inhibiting vertical movement of the front body section relative to the main vehicle; for the hitch and coupler connection to be a hinge-type connection with one of the hitch and coupler comprising a vertical pivot axis that enables horizontal movement of the front body section relative to the main vehicle while inhibiting vertical movement of the front body section relative to the main vehicle.

The main vehicle may hâve a factory-in hitch, with the coupler of the auxiliary trader being configured for hitching to the particular hitch. Altematively, the main vehicle may be retrofitted with a hitch arranged to correspond with the coupler of the auxiliary trader.

Further features provide for the at least one linear actuator to be located at an elevated position relative to the hinge connection between the front and rear body sections, the variable force being a variable pushing force that urges an upper part of the rear body section away from the front body section, thereby inducing a torque about the pivot axis that urges the at least one axle toward a ground surface; and for the upper part of the rear body section to hâve a slanted surface facing the at least one linear actuator and against which the at least one actuator presses.

Further features provide for the at least one linear actuator to be further arranged to selectively induce an opposite torque on the rear body section about the pivot axis that urges the at least one axle away from a ground surface such as to raise wheels mounted on the at least one axle of the rear body section above the ground surface.

Further features provide for the auxiliary trader to include a First group of at least one linear actuator arranged to cause a variable torque in a First direction about the pivot axis of the hinge connection that urges the at least one axle towards the ground surface, and a second group of at least one linear actuator arranged to induce a torque in a second, opposite direction on the rear body section about the pivot axis of the hinge connection that urges the at least one axle away from the ground surface such as to raise wheels mounted on the at least one axle of the rear body section above the ground surface.

Further features provide for the First group of one or more linear actuators to be located at an elevated position relative to the hinge connection between the front and rear body sections, the variable force being a variable pushing force that causes the First torque, and for the second group of one or more linear actuators to be located at an lowered position relative to the hinge connection between the front and rear body sections, the variable force being a variable pushing force that causes the second torque in the opposite direction as that of the First torque.

Further features provide for the First group of linear actuators to include between 2 and 5 linear actuators, preferably 4; and for the second group of linear actuators to include between l and 3 linear actuators, preferably l.

A further feature provides for the at least one linear actuator to be an air spring.

In accordance with a further aspect of the invention there is provided a method of reducing the per-axle load of a main vehicle:

hitching a coupler provided on a front body section of an auxiliary trader to the main vehicle, the connection of the coupler to a hitch of the main vehicle being configured to inhibit vertical movement of the front body relative to the main vehicle, the auxiliary trader further including a rear body section with at least one axle and that is articulatedly connected to the front body section about a hinge connection, the hinge connection having a pivot axis substantially parallel to the at least one axle;

operating one or more linear actuator provided on one or both of the front and rear body sections to exert a variable force on the other of the front or rear body sections, a force vector of the variable force of the one or more linear actuator being offset from the at least one axle; and thereby inducing a variable torque about the pivot axis that exerts a variable force on the at least one axle urging the at least one axle toward a ground surface, wherein the variable force exerted on the at least one axle transfers a portion of the weight of the main vehicle onto the at least one axle of the auxiliary trader.

An embodiment of the invention will now be described, by way of example only, with référencé to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
	In the drawings: Figure l	is a side élévation of a first embodiment of an auxiliary trader in
5	Figure 2	accordance with the invention hitched to a semi-trailer; is an enlarged area of Figure l;
	Figure 3	is a front perspective view of the auxiliary trader of Figure l;
10	Figure 4	is a rear perspective view of the auxiliary trader of Figure l;
	Figure 5	is a side élévation of the auxiliary trader of Figure l illustrating forces
15	Figure 6	and torque exerted on various components of the auxiliary trader; is a top view of the auxiliary trader of Figure l ;
	Figure 7	is a partly exploded view front perspective view of the auxiliary trader
20	Figure 8	of Figure l; is a partly exploded view rear perspective view of the auxiliary trader of
	Figure 9	Figure l; is a partly exploded side élévation of the auxiliary trader of Figure l;
25	Figure 10	is a partly exploded top view of the auxiliary trader of Figure l ;
	Figure 11	is a flow diagram of a method for reducing the per-axle load of a vehicle;
	Figure 12	is a partly exploded side view of a second embodiment of an auxiliary
30		traiter;
	Figure 13	is a front perspective view of the auxiliary trader of Figure 12;

Figure 14 is a top plan view of the auxiliary trader of Figure I2;and

Figure 15 is a section view along the line XV-XV shown in Figure 14.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

An embodiment of an auxiliary trader in accordance with the invention is described below. Directional référencés such as front and rear refer to directions towards a front end of a vehicle and a rear end of a vehicle, respectively. Référencés to horizontal and vertical assume the objects in question are positioned on a fiat and level surface.

The auxiliary traiter includes two main parts: a front body section and a rear body section. The front body section includes a coupler for hitching the auxiliary trader to a hitch of a main vehicle, such as a semi-trailer for example. In other embodiments, or merely other use cases, the main vehicle may also be any other vehicle to which the auxiliary trader is hitched, including a non-articulated or rigid truck. The connection formed by the coupler and hitch (when hitched) is such that the auxiliary trader can move in the horizontal relative to the main vehicle (i.e. pivot horizontally at the coupler/hitch connection), but inhibiting vertical movement of the auxiliary trader relative to the main vehicle. This implies that vertical forces on the coupler of the trader will also be exerted on the hitch and thus the châssis of the main vehicle.

The rear body section includes the axle unit of the auxiliary trader and has at least one axle. The rear body section is articulatedly connected to the front body section about a hinge connection. This hinge connection has a pivot axis that is substantially parallel to the axle or axles, and thus substantially horizontal when the trader is positioned on a fiat and level surface. This implies that the rear body section can pivot in the vertical relative to the front body section and therefore also relative to a main vehicle when the auxiliary trader is hitched to a main vehicle.

The front or rear body section includes at least one linear actuator. The linear actuator or actuators are arranged to exert a variable force on the other of the front or rear body sections. This, in turn, induces a variable torque about the pivot axis of the hinge connection that connects the front and rear body sections. The variable torque urges the axle or axles toward a ground surface, on which the wheels of the axle or axles rests, translating into a variable force exerted by the wheels on the ground surface. A corresponding reaction force is exerted on the wheels and due to their mechanical connections also on the front body section, hitch, and thus the main vehicle to which the auxiliary trader is hitched.

This causes the weight on the axles of the main vehicle to be partly shifted on the axle or axles of the auxiliary trader, which is controlled through the variable force of the linear actuator.

Depending on the position of the linear actuator or actuators relative to the hinge connection between the front and rear body sections, the variable force required to induce a torque about the hinge connection may be either a variable pulling force, or a variable pushing force. In embodiments in which the linear actuators are positioned operatively below the hinge connection, a variable pulling force may be required so that the direction of the torque is such that it urges the axle or axles of the auxiliary traiter toward a ground surface. Conversely, in embodiments in which the linear actuators are positioned operatively above the hinge connection, a variable pushing force may be required so that the direction of the torque is such that it urges the axles of the auxiliary trader towards a ground surface. The direction of the force vector of the variable pulling or pushing force, as the case may be, is offset from the axle or axles of the auxiliary trader (i.e. the force vector does not intersect the axle. This means that no adaptation of the axle assembly itself is required, and that a stock standard axle unit may be used on the auxiliary trader.

In some embodiments, the auxiliary trader may hâve two groups of linear actuators. The First group may be responsible for the (first) torque and associated forces that urge the axles toward the ground, thereby shifting some of the load of the main vehicle onto the axle or axles ofthe auxiliary trader. Such embodiments may further inciude a second group of linear actuators that are responsible for a (second) torque, in an opposite direction of the first torque, which may be utilised to lift the wheels fitted onto the axle or axles of the auxiliary trader off the ground when it is not in use.

To utilise the first torque (i.e. to shift the load of the main vehicle), the second group of linear actuators may be deactivated, de-energised, or otherwise incapacitated so that they exert no (or very little) torque and force and not oppose the first torque. Conversely, to utilise the second, opposite torque (i.e. to lift the wheels of the auxiliary trader off the ground), the first group of linear actuators may be deactivated, de-energised, or otherwise incapacitated so that they exert no (or very little) torque and force and not oppose the second torque. In embodiments where the linear actuators are air springs, deactivating, deenergising or otherwise incapacitating the air springs would be achieved by relieving the air pressure in the air springs, allowing it to expand and contract (akin to a concertina).

Figures l to 10 show a first embodiment of an auxiliary trader (100) in accordance with the invention. Figure l and the enlarged view of Figure 2 show the traiter (100) hitched to a main vehicle (10) which, in this particular example, is a semi-trailer (12) drawn by a truck tractor (14). The hitch assembly (l 10) by means of which the auxiliary trader (100) is hitched to the semi-trailer (12) includes a hitch (l 12) retrofitted to the semi-trailer and a coupler (H4) that is releasably securable to the hitch. The auxiliary trader (100) may be easily hitched and unhitched to and from the main vehicle (10) depending on whether the payload weight of the main vehicle requires the additional axle or axles of the auxiliary traiter.

The auxiliary traiter (l 00) is comprised of two major parts: a front body section (l20) and a rear body section (l 40). The coupler (l 14) is provided at a front end of the front body section ( 120), with a drawbar beam (122) extending substantially horizontally and rearwards from the coupler towards an upright mounting plate ( 124). Triangular reinforcement plates (126) are welded into the junction of the drawbar beam (122) and the mounting plate (124).

A hinge connection (128) connects the rear body section (140) to the front body section (120) at the mounting plate (124). The hinge connection (128) has a pivot axis substantially parallel to an axle (142) of the auxiliary trader provided on the rear body section (140). The pivot axis of the hinge connection will therefore be orientated substantially horizontally when the auxiliary traiter is positioned on a fiat and level surface.

The rear body section (140) further includes a châssis (144) comprising two longitudinal châssis beams (146), and is supported at the rear by an axle unit consisting of one or more axles. In the présent embodiment of the auxiliary trader ( 100), the axle unit includes a single axle (142).

Three spaced apart linear actuators are mounted onto a rear face ( 125) of the mounting plate (124) at an elevated position relative to the axle (142) and, more particularly at an elevated position relative to the hinge connection (128) that articulatedly connect the front body section (120) and the rear body section (140). In the présent embodiment, the linear actuators are air springs (148) that may be connected to a pneumatic System of a main vehicle to which the auxiliary trader is hitched. In other embodiments the auxiliary traiter may hâve an independent pneumatic System.

An abutment plate (152) is provided atop the châssis (144). The abutment plate (152) comprises a generally upright abutment plate (152) with the face (l 53) of the abutment surface being angled slightly rearwards. That is to say that an upper edge of the abutment plate (152) is slightly rearward relative to a lower edge thereof. Triangular reinforcement plates (154) are provided at a junction of the châssis beams ( 146) and the abutment plate (152).

The air springs (148) are mounted in an orientation to expand in a generally rearward direction from the rear face (125) of the mounting plate (124) when air pressure to the air springs are increased, and their opposite ends abut the face ( 153) of the abutment plate ( 152).

Referring now to Figure 5, the air pressure to the air springs (148) may be varied so as to exert a variable pushing force (Fas) onto the abutment plate (152). The pushing force from the air springs (Fas) is exerted onto the abutment plate (152) at an elevated position relative to the hinge connection (128), causing a variable torque (Th) about the hinge connection (128) that connects the front body section (120) and the rear body section (140). The direction of the torque is clockwise as viewed from the side shown in Figure 5, and thus urges the rear end of the rear body section (140), and thus also the axle (142), towards the ground surface (160). Where tyres (143) of wheels mounted onto the axle (142) rests on the ground surface (160), a force (Faxle) is exerted on the ground surface comprising a weight (Fatw) of the auxiliary trader (100) as well as a variable vertical component (Ft) of a force on the axle caused by the variable torque (Th).

As is clear by the direction of the force vector (Fas) of the air springs ( 148), this force does not intersect with the axle ( 142), and is therefore offset from the axle.

Therefore, increasing the variable force (Fas) of the air springs ( 148) increases the variable torque (Th) which, in turn, increases the total magnitude of Faxle. An equal but opposite reaction force (Fr) is exerted on the auxiliary trailer (100) by the ground surface (160). Since the hitch assembly (l 10) inhibits vertical movement of the front body section (l 20) relative to the main vehicle (l 0), a variable upward force (Ft) is also exerted on the hitch of the main 10 vehicle (l 2).

This effectively transfers some of the weight on axles of the main vehicle (12) onto the axle (142) of the auxiliary trailer (100). This, in turn, may distribute the total weight of the payload over the additional axle (or axles) of the auxiliary trailer, lowering the per-axle load 15 of the vehicle as a whole.

The auxiliary trailer in accordance with the invention may be used in a method (200) for reducing the per-axle load of a vehicle. Referring now to Figure 11, the method includes hitching (202) the coupler (H4) provided on a front body section (120) of the auxiliary ' 20 trailer (100) to the vehicle (12), the connection of the coupler and hitch being configured to inhibit vertical movement ofthe front body relative to the vehicle. The auxiliary trailer (l 00) includes a rear body section (140) with at least one axle (142) and is articulatedly connected to the front body section ( 120) about a hinge connection (128). The hinge connection (128) has a pivot axis substantially parallel to the at least one axle (142).

One or more linear actuator (148) provided on one or both of the front (120) and rear ( 140) body sections is operated (204) to exert a variable force (Fas) on the other of the front or rear body sections. A force vector of the variable force (Fas) is offset from the at least one axle (142).

A variable torque (Th) is induced (206) about the pivot axis ( 128) that exerts a variable force (Ft) on the at least one axle, urging the at least one axle toward a ground surface. The variable force exerted on the at least one axle (142) transfers (208) a portion of the weight of the vehicle onto the at least one axle of the auxiliary trailer.

Figures I2 to 15 show a second embodiment of an auxiliary trailer (200) in accordance with this invention. Like reference numerals to those in Figures l to 10 refer to like features in the first embodiment ( 100).

In this embodiment, the auxiliary trailer has a First group of linear actuators and, more particularly, a First group of air springs (202). This First group of air springs (202) are essentially similar to the air springs (148) of the first embodiment, except that they are an array of four air springs, whereas the First embodiment had only three. Their functionality will therefore not be repeated here in the interest of conciseness.

Referring now to the section view XV-XV in Figure 15, the reason for the additional air spring in this second embodiment of the auxiliary trailer (200) will become apparent. In certain applications, the main vehicle (20) (shown in broken lines) may hâve a longer overhang. The présent embodiment of the auxiliary vehicle (200) makes provision for this application in lowering the mounting plate (124) and the abutment plate (153). This, in turn, reduces the radial distance between the hinge connection (128) and the air springs (202). With only three air springs, the same force (Fas) would therefore resuit in a smaller torque (Th). To compensate for the reduced distance between the hinge connection (128) and air springs (202), an additional air spring is therefore added to increase the applied force (Fas), thus resuiting in the same torque (Th).

This auxiliary trailer (200) also includes a second group of linear actuators and, more particularly, also an air spring (204). For convenience reference will be made to the “lower air spring”. Although there is only one air spring in the second “group” of air springs, it forms a separate functional group from the first group of air springs (202).

The lower air spring (204) is mounted to the mounting plate (124) below the hinge connection (128). Therefore, and as shown more clearly in Figure 15, a pushing force (Fl) exerted by the lower air spring (204) against a lower abutment plate (206) on the rear body section will resuit in a torque (Tl) about the hinge connection (128) in an opposite direction. This torque (TL) urges the axle (142) away from the ground surface (160) and ailows the wheels (143) to be raised off the ground surface. This may be desired if the load carrying ability of the auxiliary trader (200) is not immediately required.

It will be appreciated that in order to operate the lower air spring (204) and elevate the wheels (142), the first group (202) (or “upper air springs”) need to be depressurized so as not to provide an opposing force and torque. Similarly, when the upper air springs (202) are operated, so as to shift some of the load of the main vehicle (20) onto its axle (142), the lower air spring (204) will need to be depressurized, so not so interfère with an opposing force and torque.

The invention therefore provides a means of transferring load carried by a main vehicle (e.g. a semi-trailer) axle unit to the axle or axle unit of the auxiliary trader, which is hitched behind the main vehicle, thereby increasing the payload while maintaining per-axle loads within physical and regulatory limits.

The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the précisé forms disclosed. Persons skilled in the relevant art can appreciaté that many modifications and variations are possible in light of the above disclosure.

The language used in the spécification has been principally selected for readability and instructional purposes, and it may not hâve been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any daims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following daims.

Finally, throughout the spécification and accompanying daims, unless the context requires otherwise, the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims (12)

1. An auxiliary trailer comprising:

a front bocly section having a coupler arrangée! to be hitched to a hitch of a main vehicle, with the connection of the coupler and hitch inhibiting vertical movement of the front body relative to the main vehicle, and a rear body section with at least one axle and that is articulatedly connected to the front body section about a hinge connection, the hinge connection having a pivot axis substantially parallel to the at least one axle, wherein either or both of the front and rear body sections includes at least one linear actuator arranged to exert a variable force on the other of the front or rear body sections to thereby induce a variable torque about the pivot axis that in tum exerts a variable force on the at least one axle that urges the at least one axle toward a ground surface and transfers a portion of the weight of the main vehicle onto the at least one axle of the auxiliary trailer, and wherein a force vector of the variable force is offset from the at least one axle.

2. The auxiliary trailer as claimed in claim 1 wherein the hitch and coupler connection are articulated so as to enable horizontal movement of the front body section relative to the main vehicle while inhibiting vertical movement of the front body section relative to the main vehicle.

3. The auxiliary trailer as claimed in claim 1 or 2 wherein the hitch and coupler connection forms a hinge-type connection with one of the hitch and coupler comprising a vertical pivot axis that enables horizontal movement of the front body section relative to the main vehicle while inhibiting vertical movement of the front body section relative to the main vehicle.

4. The auxiliary trailer as claimed in any one of the previous daims wherein the at least one linear actuator is further arranged to selectively induce an opposite torque on the rear body section about the pivot axis that urges the at least one axle away from a ground surface such as to raise wheels mounted on the at least one axle of the rear body section above the ground surface.

5. The auxiliary trader as claimed in any one of the previous daims wherein the at least one linear actuator is located at an elevated position relative to the hinge connection between the front and rear body sections, the variable force being a variable pushing force that urges an upper part of the rear body section away from the front body section, thereby inducing a torque about the pivot axis that urges the at least one axle toward a ground surface.

6. The auxiliary trader as claimed in claim 5 wherein an upper part of the rear body section has a slanted surface facing the at least one linear actuator and against which the at least one linear actuator presses to exert the variable pushing force.

7. The auxiliary trader as claimed in any one of daims l to 3 including:

a first group of at least one linear actuator arranged to cause the variable torque in a first direction about the pivot axis of the hinge connection that urges the one or more axle towards a ground surface, and a second group of at least one linear actuator arranged to induce a second torque in an opposite direction on the rear body section that urges the at least one axle away from a ground surface such as to raise wheels mounted on the at least one axle above the ground surface.

8. The auxiliary trader as claimed in claim 7 wherein the first group of one or more linear actuator is located at an elevated position relative to the hinge connection between the front and rear body sections, the variable force being a variable pushing force that causes the variable torque, and for the second group of one or more linear actuators to be located at a lowered position relative to the hinge connection between the front and rear body sections, and causing a pushing force that causes the second torque.

9 The auxiliary trader as claimed in claim 7 or 8 wherein the first group of linear actuators includes between 2 and 5 linear actuators, and wherein the second group of linear actuators includes between l and 3 linear actuators.

10 The auxiliary trader as claimed in claim 9 wherein the first group of linear actuators include 4 linear actuators, and wherein the second group of linear actuators includes l linear actuator.

11. The auxiliary trader as claimed in any one of the previous daims wherein the linear actuators are air springs.

12. A method of reducing the per-axle load of a main vehicle:

hitching a coupler provided on a front body section of an auxiliary trader to the main vehicle, the connection of the coupler to a hitch of the main vehicle being configured to inhibit vertical movement of the front body relative to the main vehicle, the auxiliary trader further including a rear body section with at least one axle and that is articulatedly connected to the front body section about a hinge connection, the hinge connection having a pivot axis substantially parailel to the at least one axle;

operating one or more linear actuator provided on one or both of the front and rear body sections to exert a variable force on the other of the front or rear body sections, a force vector of the variable force of the one or more linear actuator being offset from the at least one axle; and thereby inducing a variable torque about the pivot axis that exerts a variable force on the at least one axle urging the at least one axle toward a ground surface, wherein the variable force exerted on the at least one axle transfers a portion of the weight of the main vehicle onto the at least one axle of the auxiliary trader.