EP0000979B1

EP0000979B1 - Rigid axle suspension system for a vehicle

Info

Publication number: EP0000979B1
Application number: EP78300217A
Authority: EP
Inventors: Timothy Selwyn Fry
Original assignee: GKN Group Services Ltd
Current assignee: GKN Group Services Ltd
Priority date: 1977-08-13
Filing date: 1978-07-31
Publication date: 1981-09-23
Also published as: DK356078A; US4278270A; JPS5433424A; CA1082234A; DE2861114D1; BR7805157A; AU3871178A; EP0000979A1; ES472503A1; AU528813B2

Description

This invention relates to vehicles having sprung rigid axles.
In a vehicle having a rigid axle which is conventionally sprung using leaf springs, the characteristics of the spring-restoring force in bump and in roll are usually dissimilar. By "bump" we mean that both ends of the axle are deflected during travel of the vehicle through substantially the same distance perpendicular to a reference plane of the body or chassis of the vehicle and by "roll" we mean that one end of the axle is deflected relative to the other in directions perpendicular to said reference plane. When the vehicle stands on a horizontal surface the reference plane will be horizontal. Thus for a given deflection of the axle relative to the reference plane in bump the spring-restoring force will be greater than that if one end of the axle should be deflected by the same distance i.e. in roll. This is because it is not normally practicable to arrange the springs over the wheel centres. If, for example, leaf springs are arranged halfway between the axle centre and the wheel centres, the spring-restoring force will only be one-quarter in roll of that which it is in bump, assuming the same deflection of the wheel or wheels. This is because in roll the springs deflection will only be one-half of that of the deflected wheel and the restoring moment arm will also only be one-half of what it would be were the springs arranged over the wheel centres.
Moreover, the axial displacement of the spring-restoring force and the wheels induces large bending moments in the axle which has to be of massive construction to withstand these moments.
There have been proposals for the mounting of a rigid axle relative to a vehicle chassis by various configurations of linkage. For example, French patent specification 992,744 discloses, in Figures 4-6, the suspension of a rigid axle relative to a vehicle by torsion bars on the chassis, operating on outwardly extending arms which are connected to the axle by rods which are articulated to the arms and axle. The axle is stabilised relative to the chassis by a transverse rod and longitudinal links at each end of the axle. However, the rods which connect the torsion bar arms to the axle are effective at positions spaced inwardly from the ends of the axle, and in terms of spring operation in bump and roll displacements are the same as a conventionally leaf sprung axle, with attendant disadvantages.
U.S. patent specification 3,069,185 discloses an air spring front end suspension for a rigid axle, in which air springs operate on an axle beam at positions spaced inwardly from the ends thereof. Accordingly, this arrangement also will suffer from relatively different spring stiffnesses in the bump and roll displacement modes. British patent specification 339,625 discloses many different arrangements of linkage for locating a rigid axle relative to a vehicle chassis, but in all such arrangements the springs are effective at positions inwardly of the axle ends, and thus also present the disadvantage above referred to. In all this prior art, there is no reference to the problem the present invention seeks to overcome.
It is an object of the present invention to provide a vehicle having a sprung axle which may be arranged to give substantially equal spring-restoring forces in bump and roll.
According to the invention we provide a vehicle comprising a chassis, a rigid axle having a wheel at each end, and a link assembly at each end of the axle comprising a first rigid link pivotally connected at one end to the axle and a second rigid link pivotally connected at one end to the chassis, the other ends of the links being pivoted together and stabilised relative to the axle or chassis, and spring means acting on the second link resiliently to support the chassis on the axle, characterised in that each first link is pivoted to the axle substantially in the centre plane of the wheel perpendicular to its axis of rotation, such that the displacement of the spring means due to a displacement, perpendicular to a reference surface on which the vehicle stands, or a predetermined point on the wheel in roll is substantially equal to the displacement of the spring means due to an equal displacement of said point in bump.
Preferably the pivotal connection between each first link and the axle lies below the rotary axis of the wheel at that end of the axle, and comprises a pivotal axis extending fore and aft of the vehicle. A ball joint may be used between said other ends of the links.
The spring means can be, for example, a coil spring acting on each second link. Alternatively the spring means can be torsion bars acting on the second links, e.g. by being arranged with their longitudinal axes coincident with the pivot axes of the second links on the chassis.
In a further arrangement each spring means may comprise a pressure transducer acting on the second link and connected by e.g. flexible pipes to a remote spring arrangement which may be variable in effect.
The link assemblies may be provided solely for springing the axle and there may be separate means for controlling the location of the axle. Alternatively, the link assemblies may be part of linkages for controlling the location of the axle.
In this latter case, each link assembly may further comprise a lower rigid link pivoted at its ends to the axle and the chassis respectively about pivot axes parallel to the length of the axle, and the second link is pivoted at said one end to the chassis about an axis inclined to said center line of the vehicle said other end of the
second link being pivotally connected to the other end of said first link.
In this construction, the upper part of the linkage acts directly at the axle ends and thus inhibits twisting of the axle during braking.
The first and second links are preferably triangular and pivoted to the axle and the chassis respectively about the bases of their respective triangles and to each other at the apices opposite to said bases. Instead of being a triangulated link, each second link can be a single arm pivoted about said inclined axis. The pivot bearings of such an arm, however, would have to be extremely strong.
If the axle carries steerable wheels then it is possible to control the castor angle of the wheels by varying the lengths of the sides of the triangulated first upper link. One may have a series of links made of different sizes or the sides themselves may be adjustable.
If one is providing linkages for a number of vehicles of different sizes, then one can control the position of the pitch centre by using first rigid links of different lengths while using other links of the same length for the different vehicles.
The axle may be driven or non-driven and the wheels thereon may be steerable or not.
The invention will now be described in detail by way of example with reference to the accompanying diagrammatic drawings in which:-

FIGURE 1 is a perspective view of one end of an axle showing a linkage embodying the invention;
FIGURE 2 is a vertical section through the arrangement shown in Figure 1;
FIGURE 3 is an elavation of the arrangement shown in Figure 1 viewed in the direction of arrow A in Figure 2; and
FIGURE 4 is a horizontal section of the arrangement shown in Figure 1.
FIGURE 5 is a horizontal section of a further form of linkage embodying the invention.
FIGURE 6 is a horizontal section of yet another linkage embodying the invention.

Referring firstly to Figure 1-4 of the drawings, a rigid axle is indicated at 10 and carries at its end a wheel 11 having a tyre 12. The wheel disc 13 is secured to a hub 14 which is rotatably mounted in wheel bearings in a support 15. The support 15 is mounted in swivel bearings located in a cup 16 at the end of the axle 10. It will be noted that there is only one swivel bearing and this is mounted wholly below the rotary axis 17 of the wheel.
The fore and aft centre line of the vehicle is indicated at 18 in Figure 1 and mounted on each side thereof is a lower rigid link 19. Each link 19 is inclined to the centre line 18 and at its forward end is pivoted to the chassis via a ball joint 20 for pivoting movement about a pivot axis 21 parallel to the axle 10. The rear end of each link 19 is pivoted by a ball joint 22 to a bracket 23 secured to the axle but inset from the end thereof. The ball joint 22 pivots the rear end of each link 19 about an axis parallel to the axle 10.
At each end of the axle is a first generally vertically extending link 24 and a second, upper, link 25. Each of these links is triangulated. The first link comprises two limbs 24a which are pivoted by ball joints 26 to the axle at a position below the rotary axis 17 and for pivotal movement about a pivotal axis 27 parallel to the centre line 18 of the vehicle.
The upper end of the link 24 is pivoted by a ball joint 28 to the outer end of the link 25. This link 25 comprises two limbs 29 and 30 pivoted at their inner ends by all joints 31 and 32 to the chassis, not shown, of the vehicle. It will be noted that the limbs 29 and 30 are of unequal length and as a result, the link 25 is pivoted about an axis 33 which is inclined to the fore and aft of the vehicle.
Figure 4 shows, at 34, the position of the tyre when the wheel is steered and it will be seen that the link 19 has to be offset to clear the wheel but the links 24 and 25 are so arranged as to give clearance to the wheel during its steering movement.
Springing means 35 acts on the limb 29 of link 25. The springing means may be a coiled compression spring or may, as shown, be a pressure transducer which is connected by flexible pipes, not shown, to a spring means whose rate may be varied.
It will be noted that the joints 26 are located in the centre plane of the wheel 11. It follows that for a given vertical displacement of a predetermined point on the wheel there will be a given displacement at the spring means 35. This will be so whether the wheel is displaced in roll or bump. This displacement of the wheel is relative to a reference plane of the vehicle chassis or body, which reference plane will, when the vehicle is standing on a horizontal surface, be horizontal. The wheel displacement perpendicular to this plane may be due either to the wheel or chassis moving in space and relative to each other.
The link 24 is pivoted to the axle 10 on the centre plane of the wheel. If one moves the pivoted axis 27 out-boardly away from the axle centre, then one will increase the roll stiffness, and if one moves the pivoted axis 27 inboardly towards the axle centre from the position shown there will be a decrease in roll stiffness.
The linkages provided by the invention enables the pitch centre of the vehicle to be determined by variations in the length and mutual relations of the links while still giving clearance to the steerable wheel as shown in Figure 4 and eliminating torsional forces in the end portions of the axle since the link 24 is pivoted to the axle adjacent the ends thereof.
As above described, the linkage which provides the characteristic of equal spring displacement whether the wheel is displaced in roll or bump forms part of a linkage which also controls the location of the axle. However, linkage as shown in Figure 5 or Figure 6 may be used for providing the required spring displacement characteristics while there is provided separate means for controlling the location of the axle. In Figure 5, a triangulated link 40 is pivoted to the chassis 41 of the vehicle about a fore and aft axis 42. This pivotal arrangement stabilizes the end 43 of the link 40 relative to the chassis. A single link 44 is connected by ball joints 45, 46 to the axle and link 40 respectively, and springing means acts on link 40 at a position 47. The position at which link 44 is pivoted to the axle correspondence to the position at which link 24 is pivoted to the axle in the arrangement of figures 1-4.
In Figure 6, a first link 50 of the same general form as the link 24 of figures 1-4 is pivoted to the axle, and a link 51 is pivoted by ball joints 52, 53 to the chassis 54 of the vehicle and link respectively. Spring means acts on link 51 at 55. This arrangement and the arrangement of Figure 5 provide for spring displacement characteristics as described in relation to figures 1-4, but require additional means for controlling axle location.

Claims

1. A vehicle comprising a chassis, a rigid axle (10 having a wheel (11) at each end, and a link assembly at each end of the axle comprising a first rigid link (24, 44, 50) pivotally connected at one end to the axle and a second rigid link (25, 40, 51) pivotally connected at one end to the chassis, the other ends of the links being pivoted together and stabilised relative to the axle or chassis, and spring means (35) acting on the second link resiliently to support the chassis on the axle, characterised on that each first link (24, 44, 50) is pivoted to the axle (10) substantially in the centre plane of the wheel (11) perpendicular to its axis of rotation, such that the displacement of the spring means (35) due to a displacement, perpendicular to a reference surface on which the vehicle stands, of a predetermined point on the wheel in roll is substantially equal to the displacement of the spring means (35) due to an equal displacement of said point in bump.

2. A vehicle according to Claim 1 further characterised in that the pivotal connection (26, 45) between each first link (24, 44, 50) and the axle lies below the rotary axis of the wheel at that end of the axle, and comprises a pivotal axis (27) extending fore and aft of the vehicle.

3. A vehicle according to Claim 2 further characterised in that each link assembly further comprises a lower rigid link (19) pivoted at its ends to the axle (10) and the chassis of the vehicle respectively about pivot axes (21) parallel to the length of the axle, and the second link (25) is pivoted at said one end to the chassis about an axis (33) inclined to the centre line (18) of the vehicle, said other end of the second link (25) being pivotally connected to the said other end of said first link (24).

4. A vehicle according to Claim 3 further characterised in that the first (24) and second (25) links are triangular and are pivoted to the axle and chassis respectively about the bases of their respective triangles and to each other at the apices opposite said bases.