GB2274629A

GB2274629A - Suspension arrangement particularly for a low floor bus

Info

Publication number: GB2274629A
Application number: GB9401437A
Authority: GB
Inventors: Simo Vuorio
Original assignee: Saab Valmet Oy AB
Current assignee: Valmet Automotive Oy
Priority date: 1993-01-29
Filing date: 1994-01-26
Publication date: 1994-08-03
Anticipated expiration: 2014-01-26
Also published as: SE9400240L; SE509475C2; FI91842B; DE4402605A1; GB9401437D0; FI930227A0; FI91842C; GB2274629B; SE9400240D0

Description

2274629 SUSPENSION ARRANGEMENT The present invention concerns a suspension

arrangement as defined in the preamble to Claim 1. 5 The object of the invention is to disclose a suspension arrangement of novel type, for use as front axle suspension in a vehicle, and specifically as front axle suspension in a low floor bus. In particular, the object of the invention is to disclose a suspension arrangement in which there occurs no harmful self-steering tendency during dynamic spring action, i.e., on the steering fulcrum is not imposed any forward/backward motion which would cause so-called self-steering movements of the steering rod and, by this route, harmful movements of the steering apparatus.

In addition, it is an object of the invention to disclose a suspension arrangement which is particularly well suited to be used in the front axle sus- pension of a low-floor bus, where the aspiration is to drop the floor level exceptionally far down, and which sunk floor causes no problems in the placement of the suspension rods comprised in the suspension arrangement.

Furthermore, it is an object of the invention to disclose a suspension arrangement in which the move ment of the front axle during spring action takes place substantially straight in vertical direction, without any lateral movement.

Furthermore, it is an object of the invention to disclose a suspension arrangement in which the caster angle increases slightly during spring action, causing in braking situation a counter-force counter acting the pitching tendency.

The suspension arrangement of the invention is characterized by that which is stated in Claim 1.

The suspension arrangement of the invention 2 comprises a pair of longitudinal suspension rods which are pivotally attached between the body, or equivalent, of the vehicle and the front axle beam, and a triangular strut which is pivotally attached between the body of the vehicle and the front axle beam, the steering arrangement of the vehicle comprising a lever affixed to the wheel body and carrying a steering joint,, to which the steering connecting rod connected with the steering apparatus is pivoted.

As taught by the invention, in order to con- trol the movement during spring action of the steering joint and of the front axle beam to be substantially vertical, and advantageously in order to enable low floor design of the vehicle, the suspension arrangement is designed to implement the principle of the so-called WATT approximative linear guide mechanism. Hereby the triangular strut is directed forward and the longitudinal suspension rods point rearward. The first pivot point of the triangular strut, or the corresponding pair of pivot points, on the front axle beam is located in a first horizontal plane, which lies at a distance below the second horizontal plane in which the second pivot points of the longitudinal pendulum rods on the front axle beam are located.

The invention affords the advantage that the suspension arrangement is appropriate to be used, in particular, to serve as front axle suspension of a low floor bus. By the invention a specially low-slung floor height has been achieved in the front axle suspension of low floor buses, which causes no problems as regards placement of the struts which belong to the suspension arrangement. At the same time, excellent lateral suspension is achieved thanks to the triangular strut.

It is a further advantage of the invention that in the suspension arrangement occurs no objection able self-steering tendency during spring action. that is. no forward/backward movement is imposed on the 3 steering fulcrum which would generate so-called self steering movements on the steering rod and, therethrough, objectionable movements of the steering apparatus.

Moreover, it is an advantage of the invention that in the suspension arrangement the movement of the front axle during spring action takes place substan tially in vertical direction, without any lateral move ment whatsoever.

It is yet another advantage of the invention that the caster angle of the steering, or the backward slant of the so-called king pin, increases slightly during spring action, producing in braking situations a force counteracting pitching tendencies.

is Other advantageous features of the suspension arrangement will be apparent in the dependent claims and in the following detailed description of an embodi ment of the invention.

In the following the invention is described in detail, referring to the accompanying drawing, wherein:

Fig. 1 presents schematically and viewed from the front, an embodiment of the suspension arrangement of the invention; Fig. 2 presents schematically and viewed from above, the embodiment of Fig. 1; Fig. 3 presents schematically and viewed from above, another embodiment of the suspension arrangement of the invention; Fig. 4 presents schematically and viewed from above, the embodiment of Figs 1 and 2; Fig. 5 presents schematically, the vehicle from below, and illustrates which angle is understood to be the rolling angle a of the wheel; and Fig. 6 shows in the form of a diagram, the variation of the wheel's rolling angle a as a function of the spring travel s, in the suspension arrangement 4 embodiment of Figs 1, 2 and 4.

In Figs 1-4 is depicted a suspension arrangement for suspension of the rigid front axle beam 1 of a vehicle, in particular of a low floor bus. The front axle is suspended in relation to the body by means of conventional air suspension known in the art, comprising air suspension elements 18.

The suspension arrangement comprises a pair of longitudinal suspension rods 2,3, pivotally disposed between the body or equivalent of the vehicle and the front axle beam 1, e.g. by means of conventional rubber joints, to serve as a longitudinal pendulum suspension. The pivot points of the longitudinal pendulum struts 2,3 in relation to the front axle beam 1 are termed the 2 1 2 second pivot points 101,10. These pivots 10 10 are in the present embodiment provided on the supporting posts 19 of the air spring elements 18, these posts extending vertically upward from the front axle beam 1. The longitudinal suspension rods 2,3 extend rearward from the front axle beam 1 and they"are oriented at a small angle against the longitudinal vertical centre-plane of the vehicle, symmetrically thereto.

The steering arrangement of the vehicle comprises a turning lever 6 attached to the wheel body 5 and carrying a steering joint 7, to which the steering rod 8 connected with the steering gear 20 of the steering apparatus is pivoted. The figures also reveal the steering knuckle tie rod 21.

The suspension arrangement further comprises a triangular strut 4, pivotally disposed between the body of the vehicle and the front axle beam 1.

In the embodiment of Figs 1, 2 and 4 the triangular strut 4 is associated with two diagonal rods 11 and 12, of equal length. The diagonal rods 11 and 12 are separate from each other, and they form an acute angle B with each other. The pivot points on the front axle beam 1 of the diagonal rods 11, 12 constitute a pair of first pivot points 91,9 2 of the triangular strut 4.

In Fig. 2 are shown two alternative modes of disposing the triangular strut 4 and the separate dia- gonal rods 11,12. Solid lines illustrate the mode in which the triangular strut 4 has been disposed so that the first pivot points on the front axle beaml of the diagonal struts 11,12, that is pivots 9 1 19 2, are located symmetrically at a distance from the longitudinal ver- tical centre-plane of the vehicle, and the pivot points 13 1 13 2 of the diagonal rods 11, 12 on the body of the vehicle are located in the immediate vicinity of the longitudinal vertical centre-plane of the vehicle, wehereby the acute angle B enclosed by the diagonal struts opens toward the front axle beam 1.

Dotted lines in Fig. 2 indicate another way in which the separate diagonal rods 11,12 can be arranged for eliciting the same effect. The triangular strut 4 is now so disposed that the first pivot points of the diagonal rods 11,12 on the front axle beam 1, points 9 1 q 2. lie close to the longitudinal vertical centre plane of the vehcile, while the pivot points 131,13 2 of the diagonal rods 11,12 on the body of the vehicle are located symmetrically and at a distance from the longi- tudinal vertical centre-plane of the vehicle, whereby the acute angle B between the diagonal struts opens away from the front axle beam 1.

Fig. 3 depicts another two embodiments regarding disposition of the triangular strut 4 in the case that the triangular strut 4 is a so-called fixed A strut; in that case two diagonal rods 14 equal in length belong to the triangular strut 4, and which enclose between themselves an acute angle B and are fixedly joined at one end at the apex 15 of the tri35 angular strut 4.

Solid lines in Fig. 3 depict an embodiment in which said triangular strut 4 serving as a fixed A 6 strut is pivoted at its apex 15 to the chassis of the vehicle with a ball joint 16, located in the longitudinal vertical centre-plane of the vehicle, and the pivot points on the front axle beam, 9 1 q 2, of the di- agonal struts lying symmetrically at a distance from the longitudinal vertical centre-plane of the vehicle, whereby the acute angle B between the diagonal struts 14 opens toward the front axle beam 1.

Another mode of disposing a triangular strut 4 serving as fixed A strut is sketched in Fig. 3, using interrupted lines. The triangular strut 4 is now pivoted by its apex 15 to the front axle beam 1 with a ball joint 17, which constitutes the first pivot point 9 of the triangular strut on the front axle beam 1, being located in the longitudinal vertical centre-plane of the vehicle, and the pivot points 131,13 2 of the diagonal rods 14 on the chassis of the vehicle are located symmetrically at a distance from the longitudinal vertical centre-plane of the vehicle, whereby the acute angle B between the diagonal struts 14 opens away from the front axle beam 1.

All the alternative modes of implementing the triangular strut 4 described in the foregoing and depicted in Figs 2 and 3 produce the same effect, that is, lateral and longitudinal suspension of the front axle beam 1. The pivot points of the triangular strut 4 form together a substantially isosceles triangle. The straight line connecting the pivot point 131,13 2; 16 of 30 the triangular strut and the pivot point 9; 91', 9 2 lies in the first plane Ti. or encloses therewith a substantially small angle. The pivots 101,10 2 of the longitudinal rods 2,3 and the pivots 221, and 22 2 by which the struts 2 and 3 are pivoted to the chassis of the vehicle are conventional rubber swivel joints. The pivots 131 and 132 of the triangular strut 4 are advantageously likewise 7 rubber swivel joints. The pivots 9, 9 1 1 9 2 and 16 of the triangular strut 4 on the front axle beam are advantageously ball joints.

With a view to controlling the movement during spring action of the front axle beam 1 to be substan tially vertical in direction, and advantageously in order to enable low floor design of the vehicle. the suspension arrangement has been disposed to implement the so-called WATT approximative linear guide princi- ple. The triangular strut 4 is forward pointing and the longitudinal suspension rods 2,3 are directed to point rearward. The first pivot point 9 of the triangular strut 4, or the corresponding pair of pivot points 9 1 19 2. on the front axle beam 1 is located in a first horizontal plane T,, which is spaced below that second horizontal plane T 2 in which the second pivot points 10 1 f 10 2 of the longitudinal pendulum struts 2,3 on the front axle beam 1 are located.

The triangular strut 4 may therefore be lo- cated at a very low level, e.g. on the level of the lower margin of the front axle beam 1, whereby the floor line in the front part of the vehicle can correspondingly be lowered down to a very low level.

As can be seen in Fig. 4, the pivot point of the pitman arm 7 is located in a horizontal, third plane T 3 between the first horizontal plane T, and the second horizontal plane T 2. In the longitudinal vertical plane of the vehicle, the pendulum radius ri of the triangular strut 4 is substantially equal to the pendu- lum radius r 2 of the longitudinal struts 2.3. The loca- tion of said third plane is about half-way between the first horizontal plane T1 and the seond horizontal plane T 2. The planes T1, T 2 and T 3 can be seen in Fig. 4; they are perpendicular against the plane of the drawing.

In the embodiments of Figs 1-4, the second pivot points 101,10 2 of the longitudinal struts 2,3 on the front axle beam 1, the pivot points 9; 91,9 2 of the 8 triangular strut 4 on the front axle beam 1 and the pivot point of the pitman arm 7 are located substan tially in the vicinity of a vertical, fourth plane T 4 ' i longitudinal and perpendicular against the longitudinal vertical centre-plane of the vehicle. The plane T 4 can > be seen in Fig. 4; it is perpendicular against the plane of the drawing.

In the longitudinal vertical plane of the vehicle, the pendulum radius ri of the triangular strut 4 may equally be substantially different in length from the pendulum radius r 2 of the longitudinal struts 2,3.

In that case the pivot point of the pitman arm, 7, is disposed in the third plane T 3 ' which lies between the first horizontal plane T. and the second horizontal plane T 2 so that when the perpendicular distance of the third plane T 3 from the first plane is 11 and that from the second plane is 1 2 ' the ratio 11/12 is substantially equal to the ratio r 2 /r 1.

As Fig. 5 reveals, the rolling angle a of the wheel in horizontal direction is the wheel angle rela tive to the longitudinal centre-line of the vehicle. In other words, the angle a is the angle of the wheel 1 s mean plane of rotation relative to the longitudinal centre-plane of the vehicle.

Fig. 6 illustrates the behaviour ofthis rolling angle of the wheel and the way in which it changes as a function of spring travel, in the front axle suspension system of the invention. Fig. 6 pre sents a coordinate system having on the vertical axis the spring travel As, in centimetres, and on the horizontal axis the change of the wheels rolling angle, Aa.

As Fig. 6 reveals, the graph runs very close to zero rolling angle throughout the spring action. The figure demonstrates that the rolling. angle does not change during spring action: it is very close to 0 all through the spring action. For instance, on spring 9 action downward in the amount of 15 cm the change of the rolling angle is only 0.01C; when downward spring action of 10 cm occurs, the change is no more than 0.0060; the change is obviously 00 for zero spring action; about 5 cm upward spring action induces 0.10 change of rolling angle. Thus no significant forward/backward movement is imposed on the steering pivot point 7 which would give rise to self-steering movements imparted to the steering rod 8 and, by this rou- te, to objectionable movements of the steering apparatus.

It has been highly common in conventional suspension arrangements that they give rise to such steering interference during spring action when the wheel moves up and down. Study of Fig. 6 teaches clearly tha t with the suspension arrangement of the invention changes of the wheel's rolling angle a during spring action can be virtually totally eliminated and that no self-steering tendency occurs.

The invention is not exclusively confined to concern the embodiment examples presented in the fore going: numerous modifications are feasible within the scope of the inventive idea defined by the claims.

Claims

1. A suspension arrangement for suspension of the rigid front axle beam (1) of a vehicle, in particu- lar of a low floor bus, comprising a pair of longitudinal suspension rods (2,3) which are pivoted between the chassis, body or equivalent of the vehicle and the front axle beam, and a triangular strut (4) pivoted between the body of the vehicle and the front axle beam of the vehicle, the steering arrangement comprising a turning lever (6) attached to the wheel body (5) and carrying a steering joint (7) to which a steering rod (8) connected to the steering apparatus is pivoted, characterized in that in order to control the movement during spring action of the front axle beam (1) to be substantially vertical, and advantageously to enable low floor design of the vehicle, the suspension arrangement is disposed to implement the principle of the so-called WATT approximative linear guiding mechanism, wherein the triangular strut (4) is forward directed and the longitudinal struts (2,3) are rearward directed, and wherein the first pivot point (9), or the corresponding pair of pivot points (91,9 2) of the triangular strut (4) on the front axle beam is located in a first horizontal plane (T1) which lies at a distance below that second horizontal plane (T 2) in which the second pivot points (101,102) of the longitudinal pendu lum suspension rods (2,3) on the front axle beam are located.

2. Suspension arrangement according to claim 1, characterized in that the pivot point of the steer ing joint (7) is located in a horizontal, third plane (T 3) which lies between the first horizontal plane (T1) and the second horizontal plane (T 2) ' $7

3. Suspension arrangement according to claim 1 or 2, characterized in that the second pivot points (101,102) of the pendulum struts (2,3) on the front axle beam (1), the pivot points (9; 91,9 2) of the triangular strut (4) on the front axle beam (1) and the pivot point of the steering joint (7) are located substantially in the vicinity of a vertical, fourth plane (T 4) passing through the wheel centres of the front wheels and which is perpendicular against the longitudinal vertical centre-plane of the vehicle.

4. Suspension arrangement according to claim 2 or 3, characterized in that in the longitudinal ver- tical plane of the vehicle the pendulum radius (rl) of the triangular strut (4) is substantially equal to the pendulum radius (r 2) of the longitudinal suspension rods (2,3); and that the third plane (T 3) is located about halfway between the first horizontal plane (T1) and the second horizontal plane (T 2) '

5. Suspension arrangement according to claim 2 or 3, characterized in that in the vertical plane of the vehicle the pendulum radius (r,) of the triangular strut (4) differs in length from the pendulum radius (r 2) of the longitudinal suspension rods (2,3); and that the third plane (T 3) lies between the first horizontal plane (T 1) and he second horizontal plane (T 2) in such manner that when the perpendicular distance of the third plane (T.) from the first plane is (11) and that from the second plane is (1 2) ' the ratio 11/1, is subs tantially equal to the ratio r 2 /r 1.

6. Suspension arrangement according to claim 4 or 5, characterized in that the pendulum ratios (r,) and (r.) are substantially shirter than the length (l.) of the steering rod (8).

7. Suspension arrangement according to any one of claims 1-6, characterized in that the triangular strut (4) comprises two diagonal rods (11,12) equal in length, which are separate from each other and positioned at an acute angle to each other; and that the pivot points on the front axle beam (1) of said diagonal rods (11,12) constitute a pair of first pivot 12 points (91,92) of the triangular strut (4).

8. Suspension arrangement according to claim 7, characterized in that the triangular strut (4) is so disposed that the f irst pivot points (9 1 9 2) on the front axle beam (1) of the diagonal rods (11,12) are located symmetrically at a distance from the longitudinal vertical centre-plane of the vehicle, and that the pivot points (131,13 2) of the diagonal rods (11,12) on the chassis of the vehicle are located in immediate vicinity to the longitudinal vertical centre-plane of the vehicle, whereby the acute angle B opens toward the front axle beam (1).

9. Suspension arrangement according to claim 7, characterized in that the triangular strut (4) is so disposed that that the first pivot points (91,9 2) of the diagonal rods (11,12) on the front axle beam are located in the vicinity of the vehicle's longitudinal centre-plane, and that the pivot points (131,13 2) of the diagonal rods (11,12) on the chassis of the vehicle are located symmetrically at a distance from the vehicle's longitudinal vertical centre-plane, whereby the acute angle (B) between the diagonal struts opens in the direction away from the front axle beam (1).

10. Suspension arrangement according to any one of claims 1-6, characterized in that the triangular strut (4) is a so- called fixed A strut, to the triangular strut (4) belonging two diagonal rods (14) of equal length which are disposed at an acute angle (B) relative to each other and at one end fixedly joined to each other, constituting the apex (15) of the triangular strut (4).

11. Suspension arrangement according to claim 10, characterized in that the triangular strut (4) is by its apex (15) pivoted to the chassis of the vehicle with a ball joint (16) located in the longitudinal vertical centre-plane of the vehicle, and that the pivot points (91,9 2) of the diagonal rods (14) on the 13 front axle beam are symmetrically located at a distance from the longitudinal vertical centre-plane ofthe vehicle, whereby the acute angle (B) between the dia gonal rods (14) opens toward the front axle beam (1).

12. Suspension arrangement according to claim 10, characterized in that the triangular strut (4) is by its apex (15) pivoted to the front axle beam (1) with a ball joint (17) constituting the first pivot point (9) of the triangular strut and located in the longitudinal vertical centre-plane of the vehicle, and that the pivot points (131,13 2) of the diagonal rods (14) on the vehicle's chassis are symmetrically located at a distance from the longitudinal vertical centre plane of the vehicle, whereby the acute angle (B) bet15 ween the diagonal rods (14) opens away from the front axle beam (1).

13. Suspension arrangement according to any one of claims 1-12, characterized in that the straight line connecting the pivot point (131,13 2; 16) of the triangular strut (4) and the pivot point (9: 91,9 2) is located in the first plane (T,) or encloses a substan tially small angle therewith.

14. Suspension arrangement substantially as hereinbefore described with reference to the accompanying drawings.