Rear modular suspension for a motorized heavy goods vehicle

Technical field

The invention relates to a rear suspension for a motorized heavy goods vehicle.

Background art

A suspension is generally speaking the mechanical arrangement which links an axle system (motorized axle or non-motorized axle) to a vehicle chassis.

In the field of industrial vehicles used for the transport of merchandise whose total load weight is usually greater than 3.5 tons, it is known to have a chassis incorporating two main longitudinal rails connected by cross-members. Such a chassis is calculated to sustain the heavy loads to limit bending of the chassis in a longitudinal and vertical plane. On the other hand, such a chassis usually exhibits less rigidity with respect to torsion around a longitudinal axis. Such a chassis is described in document WO2006/067551. As shown on this document, it is known to fit the rear axle or axles on such a chassis through a suspension arrangement comprising an articulated frame supporting a rigid transverse axle which carries at least one wheel at each of its two transverse extremities. The frame has two longitudinal trailing arms which are each articulated by a forward-most extremity to one of said two main rails of the chassis, and the two trailing arms are connected one to the other by a transverse beam. In WO2006/067551, the trailing arms and the beam are made of three independent parts, the transverse beam being fitted to the trailing arms at each of its extremities through an embedding connection, inhibiting any relative movement. The transverse beam described in the document is a massive part which can be made of forged steel.

A suspension frame as described in the above mentioned document is indeed very rigid transversely and very rigid against twisting around a longitudinal axis. It is therefore well adapted to equip heavy vehicles having very high payload capacities.

One object of the invention is to provide a new design for a suspension of the type above which may be suitable for a wide range of heavy goods vehicles, going from low-medium payloads (for a example 7.5 to 16 tons) up to medium-high payloads (for example 16-26 tons) or even higher. Of course, the requirements for the suspensions of so different vehicles vary, especially when it comes to the torsion rigidity of the suspension. Indeed, a very rigid suspension is of course heavier than a less rigid suspension and would be

therefore useless added weight in a lower payload truck. So, up to now, it would be provided at least two or more different suspensions designs for a same model of truck to adapt to the varying configurations of the truck, especially in terms of its maximum payload. These different designs are undesirable in terms of cost of stocks, both at the production facility level and at the after-market level, in terms of complexity of the production and in terms of flexibility to provide the client with the right truck for his needs.

Therefore, the invention seeks to provide a new design for a truck suspension which would overcome the above mentioned problems.

Summary of the invention

In view of the above objectives, the invention provides for a suspension for a heavy goods vehicle comprising a chassis incorporating two main longitudinal rails connected by cross- members, wherein the suspension comprises an articulated frame supporting a rigid transverse axle having at least one wheel at each of its two transverse extremities, wherein the frame has two longitudinal trailing arms which are each articulated by a forward-most extremity to one of said two main rails, arid wherein the two trailing arms are connected one to the other by a transverse beam, characterized in that the transverse beam is hollow, and exhibits a cavity capable of accommodating an optional transverse torsion bar, in that the cavity is open at least on one transverse side of the frame to allow insertion of the optional torsion bar, and in that the frame has means to secure the torsion bar within the cavity the frame at least against rotation around the transverse beam's main axis.

Description of figures

The following detailed description of embodiments of the invention will be better understood when read in conjunction with the appended drawings, it being however understood that the invention is not limited to the specific embodiments disclosed. In the drawings:

- Figure 1 is a schematic perspective view of a suspension arrangement according to an embodiment of the invention;

- Figure 2 is a schematic side-view of the arrangement of Figure 1 ; - Figure 3 is a more detailed perspective view of the frame of the arrangement according to the invention; and

- Figure 4 is a cross-section view of the frame though a vertical and transverse plane.

Description of the invention

On figure 1 is represented a part of a chassis of a truck having at least two longitudinal rails 10 which are connected together by transversal cross-members, not shown, according to a well known design for such vehicles. On this chassis is fitted a suspension arrangement which carries a set of wheels, ¹ not shown on the drawings. '

As can be seen on figures, the suspension arrangement comprises a frame 12 having two parallel trailing arms 14 each having a forward-most extremity 16 and a rearward-most extremity 18. Each trailing arm 14 is articulated on one of the chassis rails 10 and extends in a substantially longitudinal and vertical plane. The two trailing arms 14 are connected by a transverse beam 20. In the shown example, the transverse beam 20 joins each of the trailing arms 14 in a middle section thereof, so that the frame 12 is H shaped. Also, the trailing arms 14 and the transverse beam 20 are made of one single piece, and are in this example cast integral. Neverthelessyother designs are possible. For exemple the transverse beam and the trailing arms could be made of different parts. Preferably then, the connections of the transverse beam 20 relative to the two trailing arms 14 would then be of the embedding type, that is to say connections that allow no degree of freedom. These embedding connections could be achieved in different ways, for example by the use of keys or ribbings, or it would also be possible to weld the two ends of the transverse beam to each one of the arms.

Each of the trailing arms 14 is articulated to the chassis rails 10 through a connection bracket 22. Each connection bracket 22 is, in the example shown, a casting which exhibits a plate-like upper end with- holes 23, by which. it-is possible- to attach them, for- example with pins or with bolts, to the corresponding rail 10 of the vehicle chassis. At its lower end, each connection bracket has a yoke 24 whose two arms have a bore for a shaft 26 to pass through. This yoke 24 is used to connect the connection bracket 22 to the forward-most extremity of the trailing arm 14 in an articulated manner around a transverse axis Al. A transverse hole is in fact provided in the forward-most extremity 16 of each trailing arm 14. The connection between the connection bracket 22 and the suspension frame 12 can be achieved by engaging a shaft 26 in the bores provided in the yoke 24 and in the hole provided at the forward-most extremity 18 of each arm 14. As shown on Figure

3, the hole made at the extremity of each of the arms can be fitted with a rubber bushing 28. It should be noted that the connection between each of the trailing arms 14 and the connection bracket 22 can be considered as a ball and socket joint. Therefore, the frame 12 is articulated to the chassis around a transversal axis Al .

At their rearward-most extremity 18, each of the trailing arms 14 is connected to a rigid axle system 30 having at least one wheel (not shown) at each of its two transverse extremities. In the example shown, theiaxle system 30 comprises a rigid axle casing 32 having connection brackets 34 by which it is connected to the rearward-most extremity 18 of each trailing arm. In this example, the connection is an articulation around a transversal axis A2, similar to the connection between the connection bracket 22 and the forward- most extremity of the trailing arm 14. The axle casing 32 also has brackets for its connection to two suspension cushions 36. These suspension cushions 36 are of a well known type consisting of an elastic envelope which encloses pressurized air. These two cushions 36 are suitably connected to the pressurized air circuit of the vehicle. The top face of each of these cushions 36 can be fitted with a L shaped section 38 having one branch connected to the cushion 36 and a second perpendicular branch used for an attachment to one of the two rails 10 of the chassis. The axle casing 32 also has brackets for receiving the bottom end of a shock absorber 40. The top end of each shock absorber 40 is attached to one of the rails 10 of the chassis. It is to be noted that each shock absorber 40 is attached to the outer face of the corresponding rail, thus contributing to the overall compactness of the suspension arrangement.

As can be seen on Figures 3 and 4, the transverse beam 20 of the frame 12 is hollow, and exhibits a cavity 42 capable of accommodating an optional transverse torsion bar 44. In the example shown, the transversal beam 20 is in fact a tubular beam having a hollow cylindrical interior, which may have a section of circular shape or of many other shapes.

The cavity 42 is open on at least one transverse side of the frame 12 to allow insertion of the optional torsion bar 44. In the shown embodiment, the cavity 42 extends through the full transverse dimension of the frame and has openings 46 on both sides of the frame 12.

In the shown embodiment, each opening 46 is a circular opening having a diameter smaller than the diameter of the cavity 42. The cavity -42 is therefore limited transversally on each side by an annular flange 48 which is in fact integral with the outer wall surface of the corresponding trailing arm 14.

As shown on the figures, the cavity 42 can accommodate a transversal torsion bar 44. The frame 12 has means to secure the torsion bar on the frame at least against rotation around the transverse axis A3 of the bar 44. In the embodiment shown, the torsion bar 44, the cavity 42 and the transverse beam 20 have the same axis A3.

In the shown embodiment, the torsion bar is a cylindrical metal bar having a diameter smaller than that of the openings 46 and having a length which is bigger than the transverse dimension of the frame, so that, when inserted axially in the cavity, the bar protrudes out of the cavity at both ends. Each axial extremity 49 of the torsion bar 44 is fluted, i.e. it has axially oriented grooves. To secure the torsion bar on the frame, it is provided two end caps 50 having an axial cylindrical housing 52 and a radial annular flange 54. The cylindrical housing of each cap 50 has a fluted interior surface, matching the fluted extremities 49 of the torsion bar 44 so that they may be mounted axially on the fluted extremities 49, thereby being mechanically coupled in rotation around axis A3, without being necessarily coupled transversally along said axis A3. Alternatively, the securing means could be designed to perform an embedding connection of the torsion bar with respect to the frame, inhibiting any relative movement. In the shown embodiment, the flange 54 of each cap 50 matches the flange 48 of the cavity 42, so that they can be secured one on the other, for example by means of screws, rivets or by welding, thereby securing the torsion bar on the frame. The caps 50 ensure that, once fitted on the frame 12, the cavity 42 is closed so that no undesirable material may accumulate within the cavity 42. The caps 50 can be mounted on the frame even if no torsion bar is implemented on a specific suspension arrangement.

Indeed, the torsion bar 44 is entirely optional in the above described suspension arrangement. Its purpose is to increase the stiffness of the frame 12, especially in torsion around a longitudinal axis. Of course, the torsion bar only adds to the stiffness of the frame, which is already rigid due to its unitary construction. The overall stiffness of the frame can thus be finely tuned to match the requirements of the suspension, depending on the version of the truck on which it is to be mounted, and on how the truck is going to be used, without having to change the frame itself. The additional stiffness provided by the torsion bar can be varied by varying the diameter and/or the material of the bar. The bar can itself be hollow, to reduce its weight.

Although it is preferred to have a torsion bar extending along the whole transversal length of the frame 12, it could also be provided a shorter torsion bar. The means for securing the bar on the frame would then of course have to be adapted accordingly.

In the example shown, the means for securing the torsion bar in the cavity allow an easy dismantling of the torsion bar, without even having to remove the suspension arrangement. Therefore, it is easy to replace the torsion bar, to add a torsion bar or to remove it totally, depending on the need for a particular truck. Such replacement, addition or removal can not only be done until the last minute during the assembly process of the truck, it can also be done at any workshop during the lifetime of the truck.

Thanks to the specific location of the torsion bar 44 in the cavity 42 of the transverse 20 beam, the presence or absence of the torsion bar does change the overall space requirement of the suspension arrangement, in particular with regards with the risk of interference with other vehicle components, such as a transmission axle.

In the shown example, the cavity in the transverse beam 20 has a generally closed cross section, in that the optional torsion bar 44 can only be inserted or removed through one of the transversal openings 46 of the cavity 42. Thanks to this feature, the torsion bar is not subject to any risk of mechanical damage, which could be due to the bar being hit by a rock. Even though such a generally closed cross section cavity could exhibit some holes (such as regularly spaced holes in the tubular wall of the transverse beam), it is even preferable to have a cavity which has a fully closed cross section, especially if the cavity is sealed by the securing caps as described above, so that, the torsion bar being entirely comprised within a sealed cavity, it will be less prone to corrosion. The torsion bar being thus protected, it will give the designers more freedom to select an optimum choice of shapes and material to get the best efficiency to weight ratio for the torsion bar. For example, thanks to the fact that the torsion bar is protected against shocks by being inside a cavity, it becomes possible to make -it at least partially . from .resin _^ based composite.. materials. :

In the above described example, the cavity 42 of the frame is opened at its both transversal extremities, but it could also be provided with only one opening, such as if one the securing caps was made integral with the frame. Also, the skilled man in the art can easily design other suitable embodiments of the securing means.