Europaisches Patentamt European Patent Office Office europeen des brevets (g) Publication number: 0 435 587 A2 12 EUROPEAN PATENT APPLICATION @ Application number : 90314050.7 © Int CI.5 : B60G 5/00, B60G 11/27, B60G 17/052 (22) Date of filing : 20.12.90 (So) Priority : 23.12.89 GB 8929185 @ Inventor : Griffiths, Paul John 13 East Green, Sealand Manor, Sealand Deeside, Clwyd, CH5 2SG, Wales (GB) (43) Date of publication of application : 03.07.91 Bulletin 91/27 @ Representative : Spall, Christopher John et al BARKER, BRETTELL & DUNCAN 138 Hagley @ Designated Contracting States : Road BE DE DK ES FR IT NL Edgbaston Birmingham B16 9PW (GB) (71) Applicant : RUBERY OWEN-ROCKWELL LIMITED P.O. Box 10, Booth Street, Darlaston Wednesbury West Midlands WS10 8JD (GB) (3) Multi-axle air suspension system for a vehicle. @ A multi-axle air suspension system for a tipping vehicle having towards its near a rear axle (7'") and at least one other axle (7", T) forward of the rear axle, provides selective over-riding of the normal load equalising system between the axles during tipping so as to alleviate hogging bending moments on the vehicle's chassis. A selectively operable pressure reducing valve (41) is in circuit with a pressure air source, air springs (7C, 8C) of the rear axle (7"') and with first and second valves (23, 32), selectively operated by a third valve (39), which are in circuit with the air springs (7C, 8C ; 7B, 8B ; 7A, 8A) of the rear axle (7"') and the other axle(s) (7", 7). Operation of the first and second valves (23, 32) isolates the air springs (7C, 8C) of at least the rear axles (7"') from those of the other axle or axles (7", 7') and connects the pressure reducing valve (41) to the latter air springs (7B, 8B ; 7A, 8A) so as to lower the air pressure in those air springs. CM < oo m CO -a- CL 111 Jouve, 18, rue Saint-Denis, 75001 PARIS FIG.3. 1 EP 0 435 587 A2 2 MULTI-AXLE AIR SUSPENSION SYSTEM FOR A VEHICLE This invention relates to a multi-axle air suspen- The purpose of this invention is to provide for sion system for a vehicle. selective overriding of the normal equalisation system There has been in recent years a substantial of a multi-axle air suspension system for a vehicle so growth in the number of heavy goods vehicles which 5 that the leading axle or axles may be selectively are built with multi-axle air suspensions for the axles. loaded more lightly than the trailing axle whereby the This is because of the much improved ride character- adverse loading condition which has been described istics and equalisation of loads between axles which is alleviated. air suspension provides, as compared with mechani- The multi-axle air suspension system to which the cal spring suspensions. 10 present invention is applicable is for a vehicle having This change to air suspensions has brought to mounted towards the rear of the vehicle a rear axle light certain problems which had not previously been and at least one other axle forward of the rear axle, the apparent One such problem, aggravated by a trend system having for each of these axles a first air spring towards lightweight vehicle chassis construction in and a second air spring each adapted to be mounted order to increase useful payload, occurs on multi-axle 15 to act between a chassis of the vehicle and a respec- tipper lorries and trailers. In use the body rests on the tive end of the axle, first and second interconnecting vehicle chassis and its load is distributed along the means pneumatically interconnecting the first air chassis. When the body is tipped the load then springs and the second air springs respectively, and becomes supported between the lifting jack at the suspension levelling valve means pneumatically con- front and the pivot point of the body at the rear, which 20 nected between a source of pressure air and the first is behind the rear axle. What was formerly a distri- and second air springs and being adapted to be con- buted load along the length of the chassis then nected mechanically between an axle and the chassis becomes loading at each end of the chassis, giving of the vehicle for operation. Such a multi-axle air sus- rise to a hogging bending moment along the chassis. pension system is hereafter referred to as "a multi- Considering, for example, the case of a mechani- 25 axle suspension system of the type described". The cally suspended tri-axle trailer, when the body is tip- reference to an axle also includes a pair of aligned ped loading is transferred to the rear axle and reduced stub axles, for example as in an independent air sus- on the leading and centre axles. This is accentuated pension system, an example of which is described by the rearward movement of the centre of gravity of and illustrated in our British Patent No. 2 165 195. the load as the front of the body is raised. 30 According to one aspect of the present invention The equalisation system on a conventional multi- a multi-axle air suspension system of the type des- axle mechanical spring suspension is unable, due to cribed is provided which includes first and second frictional forces and geometrical limitations, to equal- valve means in pneumatic circuit with the first and ise the loading between the axles and the loading con- second air springs respectively of each of the axles, dition described during tipping can even result in the 35 pressure reducing valve means in pneumatic circuit wheels of the leading axle lifting clear of the ground. with a source of pressure air and with the first and sec- The situation is different with an air suspension ond valve means, and third valve means to operate because the inter-connection of the air springs for the the first and second valve means, the arrangement axles on each side of the vehicle gives much more being such that operation of the first and second valve efficient equalisation of the load between the axles. 40 means causes the air springs of at least the rear axle The result of this is that the wheels of the front axle to be isolated from the air springs of the other axle or stay on the ground and, due to the load equalisation, axles forward of the rear axle and connects the press- an upward force is applied to the chassis by the air ure reducing valve means to the air springs of said springs of the suspensions of the front, middle and axle or axles forward of the rear axle whereby the air rear axles. These forces are applied to the chassis 45 pressure in the air springs of said axle or axles forward through the lever arms represented by the distances of the rear axle is controlled at a lower pressure than of the air springs of these axles forward of the pivot in the air springs of at least the rear axle. point. Thus, the combination of increased upward The multi-axle air suspension system may loading and the associated lever arms in respect of include a "dump system" to allow selective deflation the forward and middle axle air springs further so of the air springs. The dump system may comprise increases the hogging moment applied to the vehicle fourth and fifth selectively operable valve means in chassis. This hogging moment is evidenced by signifi- pneumatic circuit between the levelling valve means cant deflection of the vehicle chassis, which is unde- and the first and second air springs respectively, and sirable. One solution to this problem would be to sixth valve means to operate the third and fourth valve stiffen the chassis but this incurs a significant weight 55 means whereby the air springs are disconnected from and cost penalty. the levelling valve means and are connected to 3 3 EP 0 435 587 A2 4 atmosphere to allow deflation of the air springs. axles 7', 7", T" — are referenced 7A, 7B, 7C from When a dump system is included as described front to rear of the trailer. Second air springs at the there is preferably also provided in circuit with it inter- other side of the trailer for the axles are referenced lock means which is operable when the fourth and fifth 8A, 8B, 8C. Thus, the leading axle T has air springs valve means are operated for deflation of the air 5 7A, 8A, the middle axle 7" has air springs 7B, 8B and springs so as to disable the third valve means, and so the rear axle T" has air springs 7C, 8C. prevent operation of the first and second valve means The conventional trailer air system includes a fil- to isolate the air springs of at least the rear axle from ter 9, brake pressure protection valve 11, air reservoir the airsprings of the other axle or axles forward of the 12, suspension levelling valve 13 and associated con- rear axle. 10 necting pipes for connecting these components According to a second aspect of the present together and to a compressor, not shown, on the trac- invention a tipping vehicle is provided which is fitted tor vehicle. with a multi-axle air suspension system in accordance As illustrated the air suspension system includes with the first aspect of the invention herein set forth. a dump system comprising pilot operated two-position An embodiment of the invention will now be des- 15 spring return valves 14, 15 (constituting fourth and cribed by way of example with reference to the accom- fifth selectively operable valve means) and a two- panying drawings in which : position manually operated pilot return dump valve 1 6 Figure 1 is a schematic drawing showing a side (constituting sixth valve means, for operating valves elevation of a towing vehicle and a tipping trailer 14, 15), shown in the "Dump" selection in which the in transport mode, 20 pilots of valves 14, 15 are connected to atmosphere Figure 2 is similar to Figure 1 but shows the trailer and the airsprings are also connected to atmosphere in tipping mode, via the valves 14, 15.