GB2034644A - Suspension system for a vehicle - Google Patents

Abstract

A suspension system for a road vehicle comprises tandem axles 10, 11 having leaf springs 12, 13 whose adjacent ends are received in pivoted equaliser beams 23. The spring bearing surfaces 24, 26 of the equaliser beams are disposed below the equaliser pivots (referring to the level position of the equaliser) so that the horizontal distances from the lines of contact between the bearing surfaces 24 and 26 and the respective springs 12, 13 to the equaliser pivots remain substantially equal throughout the normal range of travel of the equaliser. Preferably rods 30 extend between spring chairs of the trailing axle 11 and the rear portion of the equaliser beams 23 at a vertical position 31 below that at which the equaliser beams are pivoted to their hanger bracket 25. With this arrangement, the load on the respective axles remains approximately constant throughout a significant range of axle articulation. <IMAGE>

Description

SPECIFICATION Suspension system for a vehicle The present invention relates to a suspension for a heavy road vehicle such as a trailer or semi-trailer vehicle or the like.

In conventional tandem axle suspensions for heavy goods road vehicles there are employed two or more independently sprung axles spaced longitudinally of the vehicle. Load equalising interconnections are provided in an attempt to equalisethe load on the axles during normal road operation. Each axle is supported at either end on leaf springs positioned symmetrically about the longitiudinal centre line of the vehicle. The outer ends of the leaf springs are supported directly within a hanger bracket assembly secured to the vehicle and the inner ends of the leaf springs are supported within an equaliser carried in a hanger bracket secured to the vehicle, the equaliser being pivoted about a shaft parallel to the axles.

Each axle is mounted to its respective springs by means of appropriately shaped spring chairs intermediate the springs and the axle and by means of U-bolt fasteners. Each spring chair has a forward extension terminating in a yoke. The front axle is maintained in alignment transversely of the vehicle by means of radius rods pivotally connected at one end to the yoke of the respective spring chair and pivotally connected at the other end to a front hanger bracket. The or each other axle is maintained in alignment by means of radius rods pivotally connected at one end within the yoke of a respective spring chair and extending forwardly with its other end pivotally connected to an adjacent hanger bracket.

There has been a need to reconsider vehicle suspension design and in particular to provide a suspension wherein there is provision for maximum practicable axle articulation with minimum variation in axle load in order to meet national regulations specifying the maximum permitted axle load increase for a given vertical movement of one axle relative to the other axle or axles. This is achieved by lowering the spring bearing surfaces of the equaliser relative to the equaliser pivot.

Broadly stated, the invention provides a suspension system for a road vehicle comprising leading and trailing axles aranged in tandem, leaf springs secured adjacent each end of each axle via intermediate spring chairs, forward hanger brackets supported by the outer ends of the leaf springs secured to the leading axle, intermediate hanger brackets longitudinally positioned between the leaf springs and each having pivotally mounted thereon equaliser levers in which the inner ends of leaf springs attached to the leading and trailing axles are engaged and radius rods pivotally fixed to the spring chairs to maintain transverse alignment of the axles, wherein the equaliser lever has spring bearing surfaces disposed at a vertical level below the axis of the equaliser pivot when the equaliser is at its horizontal rest position such that the horizontal distances between the equaliser pivot axis and the lines of contact between the bearing surfaces and the respective springs remain substantially equal within the normal range of deflection of the equalis erfrom its rest position.

Preferably radius rods are pivotally fitted between the spring chairs of the leading axle and the respective front hanger brackets, and forwardly extending radius rods are pivotally fixed between spring chairs of the trailing axle and the rear portion of a respective equaliser at a level below that at which the equaliser is pivoted to the hanger bracket, the arrangement being such that, on braking of the vehicle, the torque applied by the leaf springs and the torque applied by the radius rods on the respective equalisers is at least partially opposed.

In this specification it should be noted that the terms leading and trailing are defined with reference to the normal direction of travel of a vehicle to which the suspension is fitted.

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 side view of a twin tandem axle suspension arrangement; and Figure 2 is a side view of a tri-axle axle arrangement.

Figures 3A and 3B are detailed sectional views on an enlarged scale of the equaliser lever and adjoining ends of the leaf springs, Figure 3A showing the equaliser lever in its level or rest position and Figure 3B showing it after upward articulation of the leading axle.

In Figure 1, a tandem axle suspension arrangement comprises a front axle 10 and a rear axle 11 secured to respective leaf springs 12 and 13 by respective spring chairs 14 and 15 and U-bolts 16 and 17. The front or outer end of the leaf spring 12 supports a spring bearing plate 18 sandwiched between front hanger bracket plates 19 secured to the vehicle. The spring chair 14 has a nose terminating in a yoke 20 to which is pivotally secured one end of a radius rod 21 whose other end is pivotally secured to the lower end 22 of the front hanger bracket. The rear or inner end of the leaf spring 12 is received within an equaliser casting 23 and a front bearing surface 24 thereof loosely rests thereon.The equaliser casting 23 is pivoted to an intermediate hanger bracket assembly 25 by means of a pivot pin (not shown) aligned transversely and a rubber bush (not shown) surrounding the pivot pin. The front or inner end of the leaf spring 13 also supports a rear bearing surface 26 of the equaliser casting and the rear or outer end thereof supports a casting 27 of a rear hanger bracket assembly 28. The spring chair 15 has a nose terminating in a yoke 29 to which is pivotally fixed one end of a radius rod 30 which extends forwardly and whose other end is pivotally fixed at 31 to or adjacent the base of the rear face of the equaliser casting 23.

The arrangement is such that, on braking, a load tending to produce clockwise rotation is imparted to the equaliser casting 23 by means of the spring 12.

This tendency to rotation is counteracted by a load tending to produ.ce anticlockwise rotation which is imparted to the equaliser 23 via the radius rod 30.

With appropriate design the two loads can be made to cancel almost completely with the result that the equaliser can maintain an approximately equal load on the two axles under a wide range of braking conditions and the tendency to "wheel hop" is reduced. It is also necessary to ensure approximately correct weight distribution between the axles when articulation due to uneven road surfaces causes relative vertical displacement between one axle and another.

To fulfil this requirement the spring contact or bearing surfaces 24 and 26 of the equaliser casting 23 are located on a level vertically below that at which the equaliser is pivoted to the hanger bracket, such that when one end of the equaliser is moved upwards about the equaliser pivot, the longitudinal or horizontal distance from the centre of pivot to a given point on the contact surface increases. This increase counteracts the horizontal movement of the line of contact between the spring and the equaliser which moves nearer to the centre of pivot because of the shape of the contact surfaces. Similarly, at the opposite end of the equaliser a given point on the contact surface moves horizontally closer to the centre of pivot of the equaliser whereas the line of contact between the spring and contact surfaces moves further from the centre of pivot.Suitable selection of the vertical distance between the centre of the equaliser pivot and the spring contact surfaces 24 and 26 when the equaliser is horizontal and of the shapes of the spring contact surfaces enables the horizontal distance from the centre of the equaliser pivot to the line of contact of the respective springs 12 and 13 at either end to remain substantially constant through a significant arc of movement of the equaliser 23. As is apparent from Figure 3A, the leading and trailing springs 12 and 13 contact respective bearing surfaces 24 and 26 at lines A and C below the pivot axis P of the equaliser lever 23. The horizontal distances h1 and h2 from the lines A and C to the pivot axis Pare equal. When the equaliser is deflected, for example to the position shown in Figure 3B, the contact lines roll to new positions B and D.However, the surface 24 has moved from a downwardly angled position to a horizontal position relative to Pso that horizontal distances are increased, this increase compensating for movement of the contact line inwardly from A two B. Similarly the surface 26 has moved to a more steeply inclined position in which the horizontal projection of the line C-P is reduced in an amount which approximately compensates for outward movement of the contact line from C to D. As a result, the contact lines remain substantially at horizontal positions h1 and h2, which assists in maintaining equal axle loads on uneven road surfaces.With the contact points A and C approximately on the same level as the pivot P, as in conventional practice, h1 does not remain equal to h2 when the equaliser lever is deflected from its normal position and uneven axle loads result.

Various modifications may be made to the embodiment described herein without departing from the invention. For example, in a tri-axle version of the suspension the centre axle may be located by means of a radius rod directly to a hanger bracket, and the leading and trailing axles may be located to equalisers. The radius rods on the leading axle are in compression rather than in tension and act in the opposite direction to the other two rods.

Such a tri-axle suspension is shown in Figure 2.

Leading, intermediate and trailing axles 60, 62, 64 are arranged one behind the other and have respective leaf springs 66, 68, 70 secured adjacent each end by means of spring chairs 72,74, 76. The front ends of leaf springs 66 are received in forward hanger brackets 78 and their rear ends are received in the front end of first equaliser casting 80 pivotaly supported in first intermediate hanger brackets 79 on rubber bushed pivot pins 85. The rear ends of equaliser castings 80 receive the front ends of intermediate leaf springs 68 and the rear ends of the springs 68 engage the front ends of second equaliser castings 82 pivotally supported on rubber bushed pivot pins 84. The front ends of trailing leaf springs 70 are received in the rear ends of equaliser castings 82 and then rear ends are supported in rear hanger brackets 86.

First radius rods 69 are pivotally secured between rearwardly directed yoke portions 73 of spring chairs 72 and pivot pins 81 in the base of the front faces of the first equalisers 80, the pins 81 being positioned below the equaliser pivot 85. Second radius rods 63 are pivotally secured between forwardly directed yoke portions 75 of spring chairs 74 and pivot pins 87 at the base of first intermediate hanger brackets 54.

Third radius rods 71 are pivotally secured between forwardly directed yoke portions 77 of spring chairs 76 and pivot pins 83 in the base of the rear faces of the second equalisers 82. The pivot pins 83 are positioned below the equaliser pivots 85. Furthermore, the spring contact surfaces of the equalisers are positioned below the respective pivot centres 84, 85 as discussed above.

The operation of the suspension is generally the same as that of the twin axle suspension described previously. Braking loads transmitted to the equalisers 80, 82 are counteracted by loads imparted thereto by the radius rods. This arrangement has been found to be satisfactory in operation, there being a reduced tendency for the ends of the leaf springs to become disengaged from the respective equalisers when the suspension passes over an uneven surface and a substantially equal vertical loading on the axles is maintained throughout the normal articulation range.

Claims (1)

1. A suspension system for a road vehicle comprising leading and trailing axles arranged in tandem, leaf springs secured adjacent each end of each axle via intermediate spring chairs, forward hanger brackets supported by the outer ends of the leaf springs secured to the leading axle, intermediate hanger brackets longitudinally positioned between the leaf springs and each having pivotally mounted thereon equaliser levers in which the inner ends of leaf springs attached to the leading and trailing axles are engaged and radius rods pivotally fixed to the spring chairs to maintain transverse alignment of the axles, wherein the equaliser lever has spring bearing surfaces disposed at a vertical level below the axis of the equaliser pivot when the equaliser is at its horizontal rest position such that the horizontal distances between the equaliser pivot axis and the lines of contact between the bearing surfaces and the respective springs remain substantially equal within the normal range of articulation of the equaliser from its rest position.

2. A suspension system according to Claim 1, wherein radius rods are pivotally fitted between the spring chairs of the leading axle and the respective front hanger brackets, and forwardly extending radius rods are pivotally fixed between spring chairs of the trailing axle and the rear portion of a respective equaliser at a level below that at which the equaliser is pivoted to the hanger bracket, the arrangement being such that, on braking of the vehicle, the torque applied by the leaf springs and the torque applied by the radius rods on the respective equalisers is at least partially opposed.

3. A suspension system according to Claim 1, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

New claims or amendments to claims filed on 7 Nov.

1979.

Superseded claims 1.

New or amended claims:

1. A suspension system for a road vehicle comprising leading and trailing axles arranged in tandem, leaf springs secured adjacent each end of each axle via intermediate spring chairs, forward hanger brackets supported by the outer ends of the leaf springs secured to the leading axle, intermediate hanger brackets longitudinally positioned between the leaf springs and each having pivotally mounted thereon equaliser levers in which the inner ends of leaf springs attached to the leading and trailing axles are engaged and radius rods pivotally fixed to the spring chairs to maintain transverse alignment of the axles, wherein the equaliser lever has spring bearing surfaces disposed at a vertical level below the axis of the equaliser pivot when the equaliser is at its horizontal rest position and shaped so that the horizontal distances between the equaliser pivot axis and the lines of contact between the bearing surfaces and the respective springs remain substantially equal within the normal range of articulation of the equaliserfrom its rest position.