GB2029781A - Air Suspension - Google Patents

Abstract

An air suspension having improved anti-roll properties may be fitted to longitudinal chassis members (50) Fig. 2 (not shown) of a goods vehicle frame or sub-frame. Brackets 2 fitted to the chassis members pivotally support rigid trailing arms (1) which can accommodate limited movement in a vertical plane. An axle 56 is secured to the trailing arms 1 at an intermediate longitudinal position. The trailing arms extend rearward of the axle and cranked outwards with their tips 42 substantially in alignment to the wheel track. Rigid air spring mounting brackets (11) extend outwards from the chassis members (50) with their tips overlying the tips 42 of the trailing arms 1 and air springs (70) are secured between them substantially in alignment with the wheel track. Load levelling valves secured to the axle control the pressure in the air springs (70). The arrangement thereby provides a high roll resistance and a high rate of spring damping for maintaining a soft ride. <IMAGE>

Description

SPECIFICATION Air Suspension The present invention relates to an air suspension for a goods vehicle, such as a semitrailer or trailer vehicle.

In the design of goods vehicles suspensions there is a conflict between the requirement of soft ride for load protection and the prime duty of the suspension which is to dampen the vibration induced by the road surface and to maintain the vehicle in a vertical attitude. This problem is specially aggravated where high centre of gravity loads are conveyed. A particular problem exists in the carriage of liquid beverages in bottle form because load breakages can occur if a sufficiently smooth ride is not achieved. Another problem area is that of partly empty liquid or bulk powder tank trailers where surging of the load is liable to occur. These problems are not easy to resolve because of variations in the condition, curvature and camber of road surfaces, which factors all have differing effects on the vehicle suspension.

In an attempt to resoive the ride problems, air suspensions have been devoloped in which the layout of the vehicle frame and axles is conventional but air suspension bellows replace the conventional leaf springs, trailing arms providing a link between the axle and the vehicle frame. Replacement of the leaf springs by air bellows and use of a load levelling valve positioned between the two wheels results in improved damping of vibration while retaining acceptable stability. However, conventional air suspensions although satisfactory for many operational purposes can be improved to provide better roll stability.

The present invention provides a suspension assembly for a goods vehicle comprising in combination: A frame or sub-frame including first and second transversely spaced longitudinally directed chassis members; first and second brackets rigidly secured to respective chassis members; first and second rigid trailing arms pivotally secured to respective brackets for movement in a vertical plane and secured at an intermediate longitudinal position to an axle, the trailing arms extending rearward of the axle and being cranked outward at their trailing ends; first and second rigid support members secured to the frame or sub-frame and projecting outwardly with their tips overlying the tips of the trailing arms; first and second air springs each secured at one end to a respective tip of a trailing arm and at its other end to an overlying tip of a support member; and load levelling valve means arranged to control the air supply to the air springs in order to maintain a constant distance between the axle and the frame or sub-frame.

The invention also provides that two or more such assemblies may be combined to form a tandem or multi-axle suspension where the load is evenly distributed between the axles through the medium of the air suspension.

Other preferred aspects of the invention are defined in the appended claims to which attention is hereby directed.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a fragmentary plan view of one side of a tandem axle suspension fitted to a vehicle frame, showing the part of a suspension which lies one side of the respective longitudinal frame member; Figure 2 is a fragmentary side elevational view of the suspension shown in Figure 1; Figure 3 is a fragmentary end view of the suspension shown in Figure 1 and of the vehicle frame which appears partly in section; and Figure 4 is an enlarged detail sectional view taken on the lines A-A of Figure 2 showing the manner of attachment of the axle to the respective trailing arm.

The suspension is shown fitted to the frame of a flat platform semi-trailer or trailer vehicle (which may further be provided with a curtain sided or TIR tilt superstructure). It will be appreciated that the same suspension can be fitted to other types of heavy goods vehicles, for example, to a subframe of a monocoque semi-trailer van or of a tank semi-trailer. The frame which is conventional for a flat platform semi-trailer includes a pair of transversely spaced longitudinal chassis members 50 which are fabricated steel I-beams and steel cross members 52 of rolled I-section which pass through regularly spaced apertures in the I-beam webs and are welded in position into the apertures. Also extending between the longitudinal chassis members are cross-members of box section (not shown) which impart torsional stability to the vehicle frame.Along the outboard ends of the cross-members 52 are fitted side raves 54. It will, of course, be realised that the frame structure to which the suspension is attached could be fabricated from other kinds of members, e.g. from box-section or channelsection longitudinal members and pressed or fabricated cross-members in arrangements appropriate to the particular kind of vehicle.

The components of the suspension are the same for each axle, so that only the components of one axle will be described. A front bearing bracket 2 comprises side plates 2a and 2b secured below the bottom flange of the longitudinal chassis member 50 with the inner plate 2b lying approximately in the plane of the web of the chassis member 50 and the outer plate 2a outboard thereof. A triangular upper gusset 27a is secured between the top of the bearing bracket 2 and the outer face of the web of the longitudinal member 50 and a lower gusset 27b is secured between the inner plate 2b and the bottom flange of the member 50.Between the plates 2a and 2b is secured a bearing pin 58 which pivotally supports the leading end of a trailing arm assembly generally designated by the reference numeral 1, a bush 33 being fitted between the pin 58 and the bearing aperture at the front end of the trailing arm assembly.

As is best seen from Figure 1, the trailing arm assembly 1 has a forward region 40 which is directed parallel to the longitudinal member 50 and to which an axle 56 is secured. Rearwardly of the tyre 60 the assembly 1 is cranked in an outboard direction to define an outwardly directed tail region whose tip 42 is approximately in line with the outside of the tyres 60. The forward region 40 has an inverted channel member 44 welded to a base plate 46 to give a box structure with projecting base flanges 47 and 48. Towards the tail of the assembly 1 , the box structure is continued and is further stiffened by an outwardly cranked upper flange plate 49. The box structure of the trailing arm assembly, especially in the forward region 40 imparts light torsional stiffness and enables the suspension to resist roll torsion.

The method of attachment of the axle 56 to the forward region 40 of the assembly 1 is apparent from Figure 4 which shows an underslung axle rrangement. An upper axle cap 51 on the top half of the axle casing is received in a chair member 53 resting on the lowerface of the base plate 46 with an intervening neoprene pad 55. A lower axle cap 57 engages the lower half of the axle casing with a further intervening neoprene pad 59. Flattened U-bolts 7 fit over the ends of the lower cap 57 which are recessed to receive them and pass through appropriately positioned fixing holed in the flanges 47 and 48, their threaded upper ends being engaged by nuts 8 to retain the axle 56 to the trailing arm assembly 1.

Cross-members 52a and 52b respectively forward and rearward of the tip 42 of the radius arm assembly 1 are provided with flanged reinforcing plates 11 extending transversely outwards from the web of the respective longitudinal member 50 to a position determined in accordance with the legally permitted maximum vehicle width. Usually this will correspond with the width dimension over the tyres because the maximum possible wheel track is adopted in most cases. Stiffening plates 12 in fore-and-aft alignment with the plates 11 are secured between the webs of the longitudinal members 50.Between the tips of adjacent plates 11 are secured first and second transversely spaced longitudinally directed frame members 18 and intermediately positioned cross-members 18a together defining a support frame for the upper end of a rolling diaphragm air spring 70 positioned with its line of action approximately on the centre line of the tyres. The lower end of the air spring 70 is bolted to the tip 42 of the radius arm 1.

Shock absorber fixing brackets 80 are fitted to the axle casing inboard of the trailing arm assembly 1 and also to the transverse reinforcing plate 12. Between the fixing brackets 80 are pivotally secured heavy duty telescopic shock absorbers 82.

It will be understood that the suspension also includes a suitable automatic self-levelling control valve 84 for either a single air spring 70 associated with single axle, or multiple air springs 70 associated with multiple axles, located adjacent thereto on each side of the vehicle on the support frame for the upper end of the air spring 70. Each control valve is operatively connected via a pivoted linkage 86 to a bracket 28 secured to the axle of the vehicle. Each valve 84 operates to admit or vent air to orfrom the respective spring 70 in response with the level of the axle 56 as perceived via the bracket 28 and linkage 86 to maintain the axle 56 in an appropriate datum position. Where there are two or more axles arranged in tandem it is usual to interconnect the air springs 70 on each side of the vehicle using only one control valve on each side.

In operation, limited vertical movement of the ends of the axles 56 in response to irregularities in the road surface is permitted by the trailing arm assemblies which pivot on their respective bearing pins 58. For tandem axle and multi air spring configurations, axle oscillation longitudinally is permitted by interconnection of pipe work between air springes. However, relative torsional movement between the axles 56 and the vehicle frame is opposed by the forward regions 40 of the trailing arm assemblies which act as torsion tubes, and it will be observed that the front bearing brackets 2 are strongly secured to the longitudinal chassis members 50 to enable such torque to be transmitted sastisfactorily.

Movement of the ends of the axle from their predetermined datum position is counteracted by appropriate adjustment of the air pressure within the air springs 70. Because the air springs are positioned well outboard of the chassis members 50 at the maximum width location, they can exert a greater righting moment than the air springs of conventional suspensions. Furthermore, the bracket 28 operating the linkage of the selflevelling control valve is also outboard of the longitudinal member 50 and the control valve is therefore more sensitive to small deflections of the axle 56 from its datum position. In consequence the suspension arrangement has a high roll resistance and a high rate of spring damping which assists in maintaining a soft ride.

The suspension is relatively simple and inexpensive and it is anticipated that it will be easy to maintain with long bearing life.

Furthermore, it is versatile and may be used for single axle suspensions and for multi-axle arrangements.

Various modifications may be made to the embodiment described herein without departing from the invention, the scope of which is defined by the appended claims. For example, an overslung axle arrangement may be adopted in place of the underslung arrangement illustrated.

Claims (7)

Claims

1. A suspension assembly for a goods vehicle comprising in combination; a frame or sub-frame including first and second transversely spaced longitudinally directed chassis members; first and second brackets rigidly secured to respective chassis members; first and second rigid trailing arms pivotally secured to respective brackets for movement in a vertical plane and secured at an intermediate longitudinal position to an axle, the trailing arms extending rearward of the axle and cranked outward at their trailing ends; first and second rigid support members secured to the frame or sub-frame and projecting outwardly with their tips overlying the tips of the trailing arms; first and second air springs each secured at one end to a respective tip of a trailing arm and at its other end to an overlying tip of a support member; and load levelling valve means arranged to control the air supply to the air springs in order to maintain a constant distance between the axle and the frame or sub-frame.

2. A suspension assembly according to Claim 1, wherein the air springs are positioned at a maximum outboard position defined by the maximum permitted vehicle width.

3. An assembly according to Claim 2, wherein the trailing arms are of enclosed hollow section and are arranged to provide torsional resistance to relative torsional movement between the axle and the body.

4. An assembly according to any preceding claim, wherein a load levelling valves associated with each air spring are secured to the respective support members and are actuated by pivoted linkage whose other ends are secured to brackets adjacent to the associated ends of the axle casing.

5. An assembly according to any preceding claim, further comprising first and following shock-absorbers mounted inboard of the longitudinal members between the axle casing and a cross-member of the frame or sub-frame.

6. An assembly according to any preceding claim, wherein two or more axles are mounted to a common frame or sub-frame, the axles being otherwise independent of one another and including pressurised air connections between the air springs on each side of the frame or sub-frame.

7. An air suspension assembly for a goods vehicle substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

7. An assembly according to Claim 6, wherein only one load levelling valve is employed on each side.

8. An air suspension assembly for a goods vehicle substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

New claims or amendments to claims filed on 23 October 1979.

Superseded claims 1-8 New or Amended Claims:

1. A suspension assembly for a goods vehicle comprising in combination: a frame or sub-frame including first and second transversely spaced longitudinally directed chassis members; first and second brackets rigidly attached to respective chassis members; first and second rigid trailing arms pivotally secured to respective brackets for movement in a vertical plane and attached at an intermediate longitudinal position to an axle, at least the portion of said arms between the pivot and the axle being of enclosed hollow section, and the trailing arms extending rearward of the axle, being cranked outward at their trailing ends and being arranged to resist at least a major portion of the relative torsional movement between the axle and the body;; first and second rigid support members attached to one or more cross-members of said frame or sub-frame, which cross-members extend the full width of the vehicle and are attached to the longitudinal chassis members, said rigid support members projecting outwardly with their tips overlying the tips of the trailing arms; first and second air springs each attached at one end to a respective tip of a trailing arm and at its other end to an overlying tip of the respective support member; and load levelling valve means arranged to control the air supply to the air springs in order to maintain a constant distance between the axle and the frame or sub-frame.

2. A suspension assembly according to Claim 1, wherein the air springs are positioned at a maximum outboard position defined by the maximum permitted vehicle width.

3. An assembly according to any preceding claim, wherein load levelling valves associated with each air spring are secured to the respective support members and are actuated by pivoted linkages whc-se other ends are secured to brackets adjacent to the associated ends of the axle casing.

4. An assembly according to any preceding claim, further comprising first and following shock-absorbers mounted inboard of the longitudinal members between the axle casing and a cross-member of the frame or sub-frame.

5. An assembly according to any preceding claim, wherein two or more axles are mounted to a common frame or sub-frame, the axles being otherwise independent of one another and including pressurised air connections between the air springs on each side of the frame or sub-frame.

6. An assembly according to Claim 5, wherin only one load levelling valve is employed on each side.