AU777361B2 - Improved trailing arm suspension - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: Actual Inventor: ANTONIO CARTA ANTONIO CARTA Address for Service: Invention Title: CULLEN CO., Patent Trade Mark Attorneys, 239 George Street, Brisbane, QId. 4000, Australia.

IMPROVED TRAILING ARM SUSPENSION Details of Associated Provisional Application: No. PQ2797 filed 13 September 1999 The following statement is a full description of this invention, including the best method of performing it known to me: This invention relates to an improved trailing arm suspension system for vehicles. In particular, the invention is directed to an improved trailing arm suspension arrangement for a trailer, although the invention is not limited thereto.

BACKGROUND ART Trailing arm suspension systems for vehicles are well known.

Examples of such trailing arm suspensions can be found in US patents 4,593,930, 4,741,553, 4,858,949 and 5,778,798.

However, a common disadvantage of trailing arm suspensions is that the pivot axis of the trailing arm is located under the chassis of the vehicle. Consequently, the chassis is elevated and the vehicle has a high centre of gravity. If the vehicle is a load-carrying trailer, the high centre of gravity makes the vehicle more susceptible to overturning on sharp corners and sloping ground. This problem is made worse if the spacing between the trailing arms of opposite wheels is significantly less than the width of the vehicle.

Another disadvantage of known trailing arm suspensions is that the arms of each pair of trailing arms do not pivot independently.

:It is also known to have more than one trailing arm on each side of the vehicle. A common disadvantage of such multiple trailing arms is that it is difficult to position the wheels on each side closely.

It is an object of the present invention to provide an improved 25 trailing arm suspension system for a vehicle such as a trailer, which overcomes or ameliorates one or more of the above disadvantages.

.l ooo* SUMMARY OF THE INVENTION cole In one broad form, the invention provides a vehicle having a chassis frame, a pair of first arms pivotably mounted to the chassis frame at respective opposite sides thereof laterally outside the frame, each first arm being pivotable about a first pivot axis transverse to the longitudinal axis of the chassis frame, a pair of second arms pivotably mounted to the chassis frame at respective opposite sides thereof laterally outside the frame, each second arm being pivotable about a second pivot axis transverse to the longitudinal axis of the chassis frame, each of the first and second arms having spring means mounted between the arm and the chassis frame, and means for rotatably mounting a wheel to the arm, wherein at each side of the frame, the first and second arms have their adjacent ends pivotally mounted to the frame, so that the first and second arms extend in opposite longitudinal directions.

The term "chassis" or "chassis frame" is intended to mean the structural support frame or beams under the body of the vehicle, but not including the wheels and their axles.

As each arm is located outside the chassis, it can be pivotally mounted to the side of the chassis so that the pivot axis is located at about the same level as the chassis frame, or even above the chassis frame.

By locating the pivot axis of the arm(s) at the same level as the 20 chassis, or thereabove, the centre of gravity of the vehicle can be kept as low as possible.

Further, as the arms on each side of the vehicle are pivotally mounted at their adjacent ends and the arms are orientated in opposite directions, the wheels on each side can be closely spaced as they do not 25 have the spring means located between them. The wheels can be mounted close to the pivot axis of their respective arms.

Typically, the vehicle is a trailer and the chassis consists of a ":.•pair of spaced parallel steel beams.

00In the preferred embodiment, each arm has one end pivotally mounted to a transverse pivot pin fixed to the chassis, and a spring mechanism at its other end. The spring mechanism is preferably an air bag spring mounted between the other (free) end of the arm and the chassis. A 3A transverse stub axis is located on each arm, and a wheel hub is rotatably mounted to the stub axle.

Preferably, the air bag spring is mounted on a platform which extends outwardly from the arm. Locating the springs outside the arms increases the stability when rocking forces are applied to the trailer. By aligning the air bag springs with their respective wheels, the forces from the ground load are transferred to more directly to the chassis via the air springs, thereby reducing twisting loads on the trailing arms.

Preferably, the arms are able to pivot independently, thereby providing semi-independent suspension.

In another form, the invention provides a trailer comprising: a chassis frame having a longitudinal axis; a first pair of wheel arms pivotably mounted to the outside of the frame at respective opposite sides thereof, and pivotable about a first pivot axis transverse to the longitudinal axis, each of the first pair of wheel arms being pivotally mounted at one end thereof to the frame and having spring means at or near its other end extending between the arm and the frame; a first pair of wheels, each rotatably mounted to a respective one of the first pair of wheel arms intermediate the ends of the respective wheel arm; a second pair of wheel arms pivotably mounted to the outside of the frame at respective opposite sides thereof, and pivotable about a second pivot axis transverse to the longitudinal axis, each of the second pair of wheel arms being pivotally mounted at one end thereof to the frame and having spring means at or near its other end extending between the arm and the frame; and a second pair of wheels, each rotatably mounted to a 25 respective one of the second pair of wheel arms intermediate the ends of the c respective wheel arm; wherein the first and second wheel arms on each side of the frame have their adjacent ends pivotally mounted to the frame, so that the second pair of wheel arms extend in an opposite longitudinal direction to the first pair of wheel arms.

In order that the invention may be more fully understood and put into practice, preferred embodiments thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a fragmentary perspective view of a trailer chassis having a trailing arm suspension according to the preferred embodiment of this invention, Fig. 2 is a perspective view similar to Fig. 1 but with the wheels omitted for clarity, Fig. 3 is a perspective view of the trailing arm suspension for one set of wheels, Fig. 4 is an end view of the chassis of Fig. 2, and Fig. 5 is a plan view of part of the chassis of Fig. 2 for one set of wheels.

DESCRIPTION OF PREFERRED EMBODIMENT As shown in the drawings, a chassis frame for a trailer or similar vehicle comprises a pair of spaced parallel beams 10 which are typically RHS steel beams. The beams 10 are joined by tie beams 10A. The chassis frame is generally planar and elongate in form, and has a longitudinal axis aligned with the normal direction of travel.

A trailing arm suspension for a first set of wheels A is mounted to the chassis. The trailing arm suspension comprises a pair of trailing arms 11, each having a respective wheel A rotatably mounted thereon. The trailing arms 11 are pivotally mounted to respective opposite sides of the chassis frame, laterally outside the frame. That is, each trailing arm 11 is mounted on the outer side of a respective beam Each trailing arm 11 has one end pivotally mounted to a pivot pin 12 held within a coupling 13 fixed to an associated beam 10. A bearing is suitably provided between each trailing arm and its pivot pin 12. Preferably, a cross beam or tie beam 10A is fixed to the beams 10 between the couplings 13 for strength and rigidity.

The pivot pins 12 are normally aligned so that the trailing arms 11 pivot about a common pivot axis which is transverse to the longitudinal axis of the trailer.

A platform 14 is provided near the other (free) end of each trailing arm 11, and extends outwardly from the arm. An air bag spring 15, or equivalent spring mechanism, is mounted between the platform 14 and an upper plate 16 which is fixed relative to the chassis frame. The upper plate 16 is supported by cantilever arms 17 extending from a plate 17A which is fixed to an associated beam 10. Overlapping guards 14A, 16A may be fitted to the platform 14 and the upper plate 16, respectively, to shield and protect the air bag 15 from accidental damage in use, or from dirt or other contamination.

As shown in Fig. 3, the free end 11A of each trailing arm 11 is located between a pair of spaced guide plates 20 which are supported from the chassis by a cantilever arm 178 extending from plate 17A. The end 11A is suitably in the form of a steel plate extension. The end 11A is sandwiched between the guide plates 20 with sufficient clearance to pivot freely up and down between the plates. However, the guide plates 20 prevent excessive side loading on the trailing arms 11, e.g. when the vehicle is turning, and keep the trailing arms parallel to the longitudinal axis of the chassis.

A stub axle 18 extends transversely outwardly from each trailing arm, at a location between the pivot pin 12 and the air bag 15. A wheel hub 19 is rotatably mounted to a respective stub axial 18. In use, a wheel or a pair of wheels is mounted to each wheel hub 19.

A shock absorber (not shown) may also be fitted between each trailing arm and the chassis frame.

The above described suspension system has several advantages over known trailing arm suspension systems, including The trailing arms are located outside the chassis frame. The pivot pins can be fixed to the sides of the chassis frame, i.e. at roughly the same level as the frame. Thus, the pivot axis of the trailing arms is generally at the same level as the chassis, rather than under the chassis as in prior art suspension systems. Consequently, the centre of gravity of the vehicle can be kept low. [If desired, the pivot pins can even be fixed above the chassis frame with suitable mountings, so that the pivot axis is above the level of the chassis frame].

The trailing arms 11, wheels and air bags are located outside the chassis. Hence, the trailing arms and their components are easily accessible for maintenance and servicing.

The wide spacing of the trailing arms 11 outside opposite sides of the chassis frame also assists in resisting twisting of the trailing arms 11, e.g. when cornering. The lateral forces on the trailing arm guide plates are thereby reduced.

Greater roll stability is achieved by locating each air bag roughly in line with its associated wheel.

10 Greater leverage is obtained by locating the air bag near the end of a relatively long trailing arm. The air bag is therefore able to respond faster, with more counteracting force. Comparatively smaller air bags could be used if desired.

With no axle beam running underneath the chassis, the superstructure may be lowered, resulting in an even lower centre of gravity. However, the trailing arm suspension system can also be used on vehicles having full beam axles.

The guide plates 20 which sandwich the moving end of each trailing arm prevent excessive side loading on the trailing arm, and keeps the arm parallel to the chassis at all times.

Each trailing arm 11 is able to pivot independently of the other, thereby resulting in a (semi) independent suspension.

The pivot pins can be formed as the outer extensions of a structural tie beam of the chassis, thereby resulting in better load distribution on the chassis as described in associated provisional application no. PQ2797.

The abovedescribed trailing arm suspension can be used for a single set of wheels, or for each set of wheels in a trailer or similar vehicle having multiple sets of wheels. (The term "set of wheels" refers to a pair of wheels located on opposite sides of the chassis).

Preferably however, if a trailer has two sets of wheels, the trailing arms of one set are orientated in the opposite direction to the trailing arms of the other set, as shown in Figs. 1 and 2. The "leading" set of trailing arms is substantially identical to the trailing set, but reversed in orientation.

(Strictly speaking, the arms in the leading set are not "trailing" arms but are referred to as "trailing arms" for consistency of expression). In Fig. 2, the elements of the leading set of trailing arms for wheels B are numbered ten higher than corresponding elements of the trailing set of trailing arms described above for wheels A.

This opposite orientation of the two sets of trailing arms helps reduce "dipping" when braking. Referring to Fig. 1, when one set of wheels A is braked, the momentum of the vehicle urges the chassis to pivot on trailing arms 11 about the axles of wheels A, in the direction shown by the arrow marked A. This would normally result in a downward movement of the chassis. However, as the second set of wheels B is braked at the same time, ::the same momentum urges the chassis to pivot on the trailing arms 21 about the axles of wheels B, in the direction shown by the arrow marked B, tending to lift the chassis. These two forces or movements substantially cancel each other out, resulting in a more stable load under sudden braking.

The foregoing describes only one embodiment of the invention and modifications which are obvious to those skilled in the art may be made thereto without departing from the scope of the invention as defined in the following claims.

For example, each trailing arm and its components can be manufactured as a modular unit for fitting to a variety of trailers, such as boat trailers and low loaders.

Claims (12)

1. A vehicle having a chassis frame, a pair of first arms pivotably mounted to the chassis frame at respective opposite sides thereof laterally outside the frame, each first arm being pivotable about a first pivot axis transverse to the longitudinal axis of the chassis frame, a pair of second arms pivotably mounted to the chassis frame at respective opposite sides thereof laterally outside the frame, each second arm being pivotable about a second pivot axis transverse to the longitudinal axis of the chassis frame, each of the first and second arms having: spring means mounted between the arm and the chassis frame, and means for rotatably mounting a wheel to the arm, wherein at each side of the frame, the first and second arms have their adjacent ends pivotally mounted to the frame, so that the first and second arms extend in opposite longitudinal directions.

2. A vehicle as claimed in claim 1, wherein the first and second pivot axes are located at about the same level as the chassis frame, or above :the chassis frame.

3. A vehicle as claimed in claim 1 or 2, wherein in each of the first and second arms, the respective pivot axis is located at one end of the arm, the spring means is mounted near the opposite end of the arm, and the wheel 25 mounting means is located on the arm intermediate the pivot axis and the spring means. i4. A vehicle as claimed in any preceding claim, wherein the spring "means is an air bag spring. A vehicle as claimed in claim 4, wherein each arm has a platform extending laterally outwardly therefrom, and an upper plate is provided above each platform in fixed relationship to the chassis frame, the air bag spring of each arm being sandwiched between its respective platform and plate.

6. A vehicle as claimed in claim 4 or 5, wherein the air bag spring of each arm is generally aligned longitudinally with the wheel associated with the respective arm.

7. A vehicle as claimed in any preceding claim further having guide means operatively associated with the free end of each arm for restricting lateral movement of the arm.

8. A vehicle as claimed in claim 7 wherein the guide means comprises a pair of spaced plates fixed relative to the chassis and located on opposite sides of a plate-like extension on the free end of the respective arm.

9. A vehicle as claimed in any preceding claim, wherein the vehicle is a trailer. A vehicle as claimed in any preceding claim, wherein the chassis frame includes a pair of parallel steel beams defining the sides of the frame.

11. A vehicle as claimed in any preceding claim, wherein each arm is pivotable about a pivot pin which forms an extension of a structural tie- oo: beam of the chassis frame.

12. A vehicle as claimed in any preceding claim, wherein each arm is pivotable independently of the other arms.

13. A trailer comprising a chassis frame having a longitudinal axis, a first pair of wheel arms pivotably mounted to the outside of the frame at respective opposite sides thereof, and pivotable about a first pivot 25 axis transverse to the longitudinal axis, each of the first pair of wheel arms being pivotally mounted at one end thereof to the frame and having spring "means at or near its other end extending between the arm and the frame, a first pair of wheels, each rotatably mounted to a respective oo one of the first pair of wheel arms intermediate the ends of the respective wheelarm, a second pair of wheel arms pivotably mounted to the outside of the frame at respective opposite sides thereof, and pivotable about a second pivot axis transverse to the longitudinal axis, each of the second pair of wheel arms being pivotally mounted at one end thereof to the frame and having spring means at or near its other end extending between the arm and the frame, and a second pair of wheels, each rotatably mounted to a respective one of the second pair of wheel arms intermediate the ends of the respective wheel arm, characterised in that the first and second wheel arms on each side of the frame have their adjacent ends pivotally mounted to the frame, so that the second pair of wheel arms extend in an opposite longitudinal direction to the first pair of wheel arms.

14. A trailer as claimed in claim 13, wherein each of the first pair of wheel arms is pivotable independently relative to the other, and each of the second pair of wheel arms is independently pivotable relative to the other and relative to the first pair of wheel arms. A trailer as claimed in claim 13 or 14, wherein each said wheel has an axis of rotation which is not substantially below the chassis frame.

16. A trailer as claimed in any one of claims 13 to 15, wherein the ooCo spring means is an air bag spring. 20 17. A trailer as claimed in any one of claims 15 to 16, wherein in each arm, its respective pivot axis is located at one end of the arm, its respective spring means is mounted near the opposite end of the arm, and its respective wheel is mounted on the arm intermediate the pivot axis and the C.o. spring means. 25 18. A trailing arm suspension substantially as hereinbefore eq described with reference to Fig. 3, or Figs. 1-2, S -e DATED this Ninth day of August 2004 coo* ANTONIO CARTA By his Patent Attorneys Cullen Co.