AXLE/SUSPENSION SYSTEMS

Abstract

An axle/suspension system (1) has an axle (5) supported from the frame of the vehicle by a pair of rigid longitudinal beams (4) pivoted to frame hangers (3). Air springs (7) and shock absorbers (8) connect between the rigid beams (4) and the frame above to control suspension movement. The axle/suspension system is particularly suited as a mid-lift axle on the tractor of a tractor-trailer vehicle. A characteristic feature is the pivotal connection (21) between each hanger (3) and beam (4), which is through a resilient bush (6) having a compliance ratiobeing a ratio of the longitudinal spring rate to the vertical spring rateof at least 10:1.

Claims

1. Axle/suspension system, for a heavy-duty vehicle having a vehicle frame with a longitudinal axis corresponding to a driving direction of the vehicle, the system comprising a vehicle axle extending transversely and having first and second ends, and a suspension assembly at each end of the axle to support the axle, each suspension assembly comprising a frame mount for fixed attachment to the vehicle frame, and a rigid longitudinal suspension beam connected fixedly to the axle at an axle/beam connection structure and connected pivotably to the frame mount through a resilient compliant bush, thereby connecting the axle to the frame mount; wherein said bush has a longitudinal spring rate and a vertical spring rate and a compliance ratio, being the ratio of the longitudinal spring rate to the vertical spring rate, of at least 10:1.

2. Axle/suspension system of claim 1 in which said compliance ratio is at least 15:1.

3. Axle/suspension system of claim 1 in which said compliance ratio is at least 25:1

4. Axle/suspension system of claim 1, in which the rigid beam is of a fabricated construction, a body of the beam being formed or assembled from one or more sheet-form or plate-form metal elements.

5. Axle/suspension system of claim 1 in which said bush provides for a vertical compliance of at least 15 mm, preferably at least 20 mm, in one or both directions of relative vertical displacement from the neutral (static) position.

6. Axle/suspension system of claim 1 in which the bush provides for a longitudinal compliance of not more than 10 mm, preferably not more than 5 mm, in one or both directions of relative longitudinal displacement from a neutral longitudinal position.

7. Axle/suspension system of claim 1 comprising an air spring mount on the upper side of the beam, the axle or the axle/beam connection structure.

8. Axle/suspension system of claim 1 which is a lift axle system, comprising a lift mechanism for lifting the axle with upward pivoting of the beams relative to the frame mounts.

9. Axle/suspension system of claim 1 in which the inside of the bush is fixed to the frame mount and the outside is fixed to the beam.

10. Axle/suspension system of claim 1 in which said bush comprises an inner mount unit comprised in or connected to one of the beam and the frame mount, an outer mount comprised in or connected to the other of the beam and the frame mount, and an elastic spring infill portion comprising one or more elastomer elements extending between the inner mount unit and outer mount and providing for resilient compliance on relative displacement thereof.

11. Axle/suspension system of claim 10 in which one or more or each of the elastomer elements comprises one or two or more rigid interleaves dividing the elastomer element into a series of sub-elements.

12. Axle/suspension system of claim 10 in which the elastic spring infill portion comprises front and rear elastomer elements extending solidly between the inner mount unit and the outer mount, and upper and lower voids defined between the inner mount unit and the outer mount.

13. Axle/suspension system of claim 12 comprising top and bottom deformable protection bumper portions facing onto the upper and lower voids to prevent direct rigid contact between the inner mount unit and the outer mount.

14. Axle/suspension system of claim 12 in which the inner mount unit and outer mount can move through at least 50%, preferably at least 70%, of their maximum vertical relative movement without abutting contact across the upper or lower void.

15. Axle/suspension system of claim 10 in which the inner mount unit defines an inner cavity containing an elastomer element and a rigid central mounting part.

16. Axle/suspension system of claim 10 in which the outer mount is connected to the beam, and engages the beam through a mechanical form engagement preventing rotation of the outer mount relative to the beam.

17. Axle/suspension system of claim 16 in which the outer mount comprises a casing having at least one circumferentially-localised outward projection engaging outwardly in a corresponding recess of the connecting structure of the beam, or at least one circumferentially-localised recess engaged inwardly by a corresponding projection of the connecting structure of the beam, to prevent rotation.

18. Axle/suspension system of claim 1 in which the bush comprises an outer casing with discrete parts which meet around the bush, the casing parts having interlock formations which overlap or interlock circumferentially to inhibit them from moving axially relative to one another.

19. Heavy-duty vehicle with a vehicle frame, comprising an axle/suspension system as defined in claim 1 with the frame mounts thereof fixed to respective frame members of the vehicle frame.

20. Heavy-duty vehicle of claim 19 in which the frame mounts are hangers depending from the frame.

21. Heavy-duty vehicle of claim 19 which is a steerable truck or tractor.

22. Heavy-duty vehicle of claim 19 in which said axle is a mid-lift or tag axle.

23. Heavy-duty vehicle of claim 18 comprising respective air springs connecting between said beams and/or axle and the vehicle frame above.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Embodiments of the present proposals are now described by way of example with reference to the accompanying drawings in which:

[0045] FIGS. 1 and 2 show a prior art construction and have already been described;

[0046] FIG. 3 is a perspective view from the front showing a trailing arm axle/suspension system embodying the invention;

[0047] FIG. 4 is a corresponding view showing the axle and beams of the system;

[0048] FIG. 5 is a perspective view showing details of a beam;

[0049] FIG. 6 is a perspective view of a first embodiment of a bush for the system;

[0050] FIG. 7 is a perspective view of a second embodiment of a bush, with a different inner mount fixing;

[0051] FIG. 8 is a perspective view of a third embodiment of a bush, with a casing interlock feature;

[0052] FIGS. 9(a) and (b) are perspective views of a bush mounting tube and of a fourth embodiment of a bush with an anti-rotation feature, FIG. 9(c) showing them assembled;

[0053] FIG. 10 is a face (axial) view of the first embodiment bush at its rest position;

[0054] FIGS. 11(a) and 11(b) show positions of the FIG. 10 bush corresponding to the lowest and highest positions of the beam end;

[0055] FIG. 12 is a cross-section of the axle showing part of an axle/beam connection, and

[0056] FIG. 13 is a front view of the axle/suspension system showing articulation and compliance of the system over an uneven surface.

DETAILED DESCRIPTION

[0057] With reference to FIGS. 3 to 5, the axle/suspension system 1 for a mid-lift axle on the tractor of a tractor-trailer vehicle comprises an axle 5 and a suspension assembly 2 at each end of the axle 5 by which the axle is supported relative to longitudinal frame members (not shown, may be conventional) extending along each side of the vehicle. Each suspension assembly 2 includes a rigid beam 4a trailing beam, in this example, although it can be a leading beam in other embodimentsconnected at its front end 41 through a pivotal connection 21 to the bottom end of a frame hanger 3 fixed to the respective frame member. The beam 4 is fixed to the axle 5 at its rear end 42.

[0058] The hanger 3 depends from a fixing plate 31 bolted to the frame in a generally known manner, and provides at its bottom end a pivot mounting 32 with a pair of spaced cheek flanges 321.

[0059] The beam 4see especially FIGS. 4 and 5is a rigid fabricated construction made from steel plate, having a box section with opposed side plates 431, a top plate 432 and a bottom plate. A cylindrical bush mounting tube 44 is fixed at the front end (pivot end) 41 of the beam by welding into circular holes at the ends of the side plates 431, with its axis horizontal. At its rear (axle end) 42 of the beam the side plates 431 have circular openings 46 receiving a body tube of the axle and fixed to it as described later.

[0060] The axle 5 is a fabricated hollow construction having a main cylindrical body tube 51, a gooseneck or crank portion 52 attached at each end carrying a spindle mounting tube 53 in which a spindle 54 for a wheel 57 is fixed. In a mid-lift axle such a gooseneck or drop provides clearance e.g. for transmission components. In other axles e.g. tag axles this may not be needed and the axle can be straight. In this embodiment the axle/suspension system 1 also incorporates brake systems for the wheels 57: details may be as known and FIG. 4 shows a torque plate 55 of this; other types of brakes may be used. Another feature of this embodiment and generally preferred herein is that the crank or drop portion 52 comprises a sleeve 521 fitting around the end of the axle and fixed to it by means of a set of complementary inward indentations of the sleeve and axle distributed circumferentially around the sleeve and axle. These indentations are formed simultaneously in sleeve and axle with the sleeve fitted around the axle e.g. as described in WO2012/044802. Desirably this axle/crank connection does not comprise any weld onto the axle.

[0061] In line with the proposals of WO2012/044802 referred to above, the axle/beam connection 25 is formed without any direct weld or bolting to the axle tube 51. As shown in FIGS. 4 and 12, a metal connector sleeve 58 fits closely around the axle tube 51 at the region to be connected, and a crimped joint 580 is created by forming a series of circumferentially-spaced indentations 582,583 around these tubes, by a compressive mechanical crimping or swaging device which indents them simultaneously, as shown in FIG. 12. The plastic deformation of the connecting sleeve indentations 582 is more than that of the axle tube indentations 583 within, so that they are then pressed together giving high strength and rigidity. The outside surface of the connecting sleeve 58 is then welded around the circular axle holes 46 in the beam to fix the axle rigidly to the beam. Because the axle tube 51 is not heat-affected by direct welding it does not suffer strength reduction and a lighter-section axle tube 51 can be used than in normal welded connections; this can reduce overall weight.

[0062] The low axis of the axle body tube 51 relative to the wheel spindles 54 in the present construction provides additional clearance for structures below the vehicle, especially for lifting the axle.

[0063] At the rear end 42 of the beam, air spring mounting points 437 with suitable fastener openings are provided along the top of each beam side plate 431. A fabricated air spring mounting platform 47 (FIG. 3) is mounted on these and supports the bottom plate 71 of an air spring 7, whose top plate 72 connects to a top mounting bracket 73 for fixing to the vehicle frame member above. The nature and role of such air springs is well-known and need not be explained further. The positions of the air springs relative to the axle and beams may vary in line with the technical context and skilled knowledge, for example the air spring may be mounted behind (beyond) the axle on an extension of or from the beam end.

[0064] Each beam 4 can be regarded as having a beam body 43 extending between the pivot end and axle end securing formations described above and having the mentioned box section. In this embodiment, the mid-part of the beam body 43 provides a mounting point 438, again with suitable fastener openings, for a discrete fabricated mount component 48 which provides a lower mounting for a shock absorber (damper) 8 whose upper end is mounted to an upper mounting 38 provided as part of the hanger 3, although it may alternatively be fixed directly to the vehicle frame. The fabricated mount component 48 on the beam also has an integral inward arm 488 constituting an upper reaction point for an axle lift mechanism 9. The lift mechanism 9 comprises an extensible lift actuator 91, such as a pneumatic actuator, operable to push up on the arm 488 of component 48 above relative to a fixed lift mounting abutment 39 below which projects from the bottom of the hanger 3. Controlled extension of the lift actuators 91 on either side of the suspension lifts the axle 5 towards the frame, with pivoting at the hanger-beam connections 21, lifting the wheels 57 out of road contact as is well known. A support cross-strut 35 connects rigidly between the bottom ends of the two hangers 3 to stabilise the structure. This strut operates to react directly lateral loads arising during vehicle turning and reduce torsional loads into the vehicle frame above.

[0065] The described construction relies largely on fabricated components, made from stock plate and tube elements by forming and joining and which can be light in weight.

[0066] Next, the characteristic pivotal connection 21 between each hanger 3 and beam 4 is described. A bush 6shown generally in FIG. 4, in more detail in FIG. 6, and schematically in operation in FIGS. 10 and 11is fixed in the bush mounting tube 44 at the front end of each beam 4. The special function of the bush 6 is to provide substantial independent vertical compliance at either side of the suspension system 1 so that the rigidity of the axle/beam assembly 4,5 does not disrupt the steering and handling of the tractor when cornering or passing over uneven ground. To this end the bush 6 provides an unusually large and soft vertical compliance, combined with the conventionally restricted longitudinal compliance necessary for stability and handling.

[0067] The main functional elements of the bushing 6 are an outer mount in the form of a cylindrical casing or shell 63, an inner mount unit 61 in the form of a generally prismatic metal block or piece 611 extending axially within the outer shell 63, and an elastomer infill 64 supporting the inner mount unit 61 coaxially with the outer shell 63. The outer shell 63 may be of steel. The elastomer elements of the infill may be formed and bonded by moulding and curing onto the metal elements, in a known manner which need not be described here.

[0068] The bushing provides for an unusually large vertical displacement, e.g. about 25 mm, and may be typically from 130 to 180 mm in diameter. The combination of low vertical stiffness with high longitudinal stiffness is achieved by front and rear elastomer elements 641 essentially confined to the regions in front of and behind the block 611 of the inner mount unit, with substantial upper and lower voids 66,67 defined between the inner mount unit 61 and the top and bottom regions of the outer shells 63. Only a small elastomer bumper piece 65 on each of the top and bottom faces 612 of the inner mount block 611 separates them. FIGS. 11(a), (b) shows the vertical displacement modes of the bush 6 showing how the front and rear elements 641, which need provide only a conventional limited longitudinal displacement (e.g. about 3 to 4 mm) which would not require large radial dimensions, must nevertheless be large in radial extent to be able to shear sufficiently to allow for the large vertical displacement. According to known principles, to distribute and limit the strain in these elements a set of metal interleaves 643 is provided to separate each element into elastomer sub-layers 642. Thus, when the bush reaches the limits of vertical displacement as shown in FIGS. 11(a) and (b) the strain in each elastomer layer 642 is limited and controlled by the division into sub-layers and the adhesion to the metal interleaves 643, enabling the large shear deformations shown without damage.

[0069] The metal block 611 of the inner mount unit 61 has convex side faces 613provided in this embodiment as an angled pair of flat facesfor efficient compression of the elastomer giving a high spring rate on longitudinal displacement. The metal interleaves 643 have correspondingly angled or bent forms to complement this shape.

[0070] According to well-known principles the bushing 6 is installed in a pre-compressed condition of the elastomer infill 64 by providing the outer shell 63 as a pair of shell parts 631 bonded on the respective elastomer elements 641. When installed the shell parts 631 form the cylindrical shell 63 with a joint line 632 where their edges meet.

[0071] A particular feature of the present embodiment is the provision of an internal bush 69 within the inner mount unit 61 itself. Specifically, the main metal block 611 of the inner unit has a central axial cylindrical through-hole 615 occupied by a rigid metal centre mount piece 617 with a cylindrical body and by an inner elastomer infill 616 which surrounds and supporting the centre mount piece 617 in the central hole for degree of resilient radial and relative rotational movement between the centre mount piece 617 and the block 611. In this embodiment the centre mount piece is a tube 617 e.g. for bolt-through mounting. FIG. 7 shows an alternative where the centre mount piece is a bar pin 618 with projecting ends for straddle mounting. The inner elastomer infill 616 is bonded to the adjacent metal components to provide resilient torsional resistance. It is a simple cylindrical sleeve, giving uniform small radial compliance in all directions. It enables the torsional response of the bushing to thegenerally smallangular movements of the beam 4 to be uncoupled to some extent from its resilient response to vertical movements of the inner unit 61 relative to the outer sleeve 63 with flexion of the main elastomer elements 641.

[0072] FIG. 8 shows a refinement in which the ends of the shell parts 631 have interlocking formationsin this case a single projection 635 on one complementing a single recess 636 on the otherso as to inhibit relative axial movement which might lead to the bush walking out of its mounting tube 44. It will be understood that a variety of different casing formations can be used to achieve this advantage.

[0073] FIG. 9 shows an optional refinement for aligning the bush 6 rotationally in its mounting and inhibiting its rotation, having in mind that the difference between its vertical and horizontal stiffness is both large and important, and the bush must be correctly oriented relative to the system and the ground. There are various ways of assuring this. In the illustrated embodiment the casing 63 of the bush is formed with a radially-displaceable spring tang 639 having outward projections 638. These can engage selectively in a corresponding slot 446 in the wall of the mounting tube 44 when the bush is assembled and mounted.

[0074] In the exemplified bushing for example the longitudinal rate may be from 40,000 to 50,000 N/mm and the vertical rate from 700 to 1400 N/mm. The ratio of longitudinal to vertical stiffness (spring rate) may be e.g. about 35:1 and this is found to give good compliance and driving performance with a mid-lift axle. Other ratios and rates may be used depending on the kind of vehicle, expected axle load and the like.

[0075] FIG. 11 shows the axle/suspension system in operation with the wheels 57 moving over uneven terrain X, and a resulting tilt in the axle 5 being accommodated by substantial vertical displacement of the pivot connection bushing 6 on the left-hand side of the figure, so that the otherwise rigid axle-beam set does not upset the vehicle frame above.

[0076] The skilled person will understand that the embodiments shown are by way of example and that a wide range of alternative embodiments is available, the scope of the invention extending in line with the general principles as understood by the skilled person from this disclosure, and taking into account also the scope of the appended claims.