IMPROVEMENTS TO MOTOR VEHICLE SUSPENSIONS

Abstract: In a suspension for motor vehicles of the type with a V-shaped axle (2), the two torque arms (8) are arranged in two directions which converge towards the rear of the motor vehicle in such a way that a transverse displacement of the central part (4) of the axle in relation to the body, caused by the transverse acceleration to which the vehicle is subjected on a bend, also causes rotation of the axle about a vertical axis in a direction which tends to oppose the steering of the vehicle. The central part (4) of the axle (2) is connected to the body by elastically-yielding connection means (5), prefer­ ably an elastic support. In relation to transverse displace­ ments of the central part of the axle, this support (5) has relatively high rigidity for deformations below a predeter­ mined value, and decreasing rigidity as deformation in­ creases beyond this predetermined value. Moreover, the elastic support (5) is shaped so that it has lower rigidity val­ ues in the transverse direction upon an increase in the verti­ cal load on the suspension. In this way, the understeering behaviour of the motor vehicle is ensured under any loading condition.

Description: Improvements to motor vehicle suspensions The present invention relates to motor vehicle suspensions of the type comprising: an axle carrying two wheels of the motor vehicle at its ends and being shaped substantially as a V disposed in a horizontal plane such that its central part is displaced towards the front of the vehicle, - elastically-yielding connection means for the articulated connection of the central part of the axle to the body of the motor vehicle about a transverse axis, a pair of torque arms each connected at one end to the body of the motor vehicle and at the opposite end to the axle, adjacent a respective end part of the latter, and resilient means interposed between the end parts of the axle 'and the body of the motor vehicle. A motor vehicle suspension of the aforesaid type is described and illustrated, for example, in the prior Italian utility model application No. 53449-B/79 and in the corresponding German Patent Application OS 30 28 124 filed by the Applicant. In designing suspensions for motor vehicles, particularly in the case of rear suspensions for front-wheel drive motor vehicles, difficulties are encountered in ensuring uniform behaviour of the motor vehicle on a bend, whatever its condition of loading. ParticulaLy in the case of front-wheel drive vehicles in which the weight of the engine bears entirely on the front axle, there is a considerable variation in the load on the rear axle according to whether the vehicle is empty or fully loaded. This is usually shown by the differing behaviour of the vehicle on a bend in that, with an increased load on the rear axle, the rear tyres are characterised by greater drift engagement, (the tyres deform more and allow greater transverse displacement of the wheel during forward movement on a bend). In more detail, because of the greater drift of the rear tyres on a bend, the motor vehicle exhibits oversteering under full loading conditions while under minimum loading conditions the motor vehicle exhibits understeering. The object of the present invention is to provide a motor vehicle suspension of the type specified initially, which will ensure a substantially uniform behaviour (and, more specifically, understeering) of the motor vehicle on a bend whatever the loading condition of the motor vehicle. The main characteristic of the invention lies in the fact that the aforesaid elastically-yielding connection means for the articulated connection of the central part of the axle to the body of the motor vehicle are shaped so as to alLow both transverse displacement of the axle and its rotation about a vertical axis, and in that the two torque arms are arranged in two directions inclined considerably to a vertical longitudinal plane in such a manner that a transverse displacement of the central part of the axle relative to the body, caused by the transverse acceleration to which the motor vehicle is subjected on a bend, will also cause rotation of the axle about a vertical axis in a direction which tends to oppose the steering of the motor vehicle. In this description and the following claims, the term "transverse refers to a direction perpendicular to the median vertical plane of the motor vehicle, whilst the term "longitudinal" refers to a direction parallel to the direction of travel of the motor-vehicle. Moreover, the terms "front" and "rear" are used with reference to the motor vehicle. In more detail, the torque arms, which have their ends aligned on a transverse axis substantially coincident with the transverse axis of articulation of the axle, are arranged in two directions converging towards the rear of the motor vehicle. By virtue of the aforesaid characteristics , it is possible (for reasons which will be explained below) to design the suspension in such a manner that the motor vehicle will always exhibit understeering on a bend, whatever its loading conditions. A further preferred characteristic of the invention lies in that, relative to transverse displacements of the central part of the axle, the elastically- yielding connection means have a relatively high rigidity for deformations below a predetermined value, and decreasing rigidity as deformation increases beyond this predetermined value. Due to this characteristic, the risk of the axle being able to rotate in the horizontal plane, even during travel in a straight line, as a result of possible transverse stresses caused by rough ground is avoided, and,moreover, there is also the result that the understeering behaviour caused by rotation of the axle in the horizontal plane will be more marked the greater the transverse accelerations are on a bend. A further preferred characteristic of the suspension according to the invention lies in the fact that the elasticallyyielding connection means have lower rigidity values in the transverse direction upon increases in the vertical load on the suspension. In this manner, the understeering behaviour brought about by rotation of the axle in the horizontal plane becomes more marked upon increases in the load on the motor vehicle, thus contributing advantageously to uniformity of behaviour on a bend, whatever the loading conditions. By virtue the aforesaid characteristics, control of axle rotation in the horizontal plane is also obtained in relation to the road holding of the rear wheels in the transverse sense. The transverse torque at the central part of the axle is, in fact, proportional to the transverse force originating in the area of contact between the rear wheels and the road surface following drift of the tyres , and this transverse force is proportional to the vertical load acting on the wheels. Further characteristics and advantages of this invention will emerge from the description which follows with reference to the accompanying drawings, supplied purely by way of non-limitative example, in which: Figure 1 is a diagrammatic plan view of a motor vehicle suspension according to the invention, Figure 2 shows the suspension of Figure 1 in a different condition of operation, Figure 3 is a diagrammatic plan view of a motor vehicle during cornering, Figure 4 is a section along the line IV of Figure 1, Figure 5 is a section along the line V of Figure 4, Figure 6 is a section along the VI of Figure 5, and Figures 7 to 9 are graphs showing the characteristics of the suspension according to the invention. In Figures 1 and 2, a rear suspension , generally indicated 1, for front-wheel drive motor vehicles includes an axle 2 carrying the two rear wheels 3 of the motor vehicle at its ends. The axle 2 is shaped substantially as a V arranged in a horizontal plane so that its central part (indicated 4) is displaced towards the front of the motor vehicle (In Figures 1 and 2 the direction of travel of the motor vehicle is shown by the arrow A). The suspension 1 further includes elastically-yielding means, comprising, in the example shown, an elastic support 5 (shown diagrammatically in Figures 1 and 2), for the articulated connection of the central part 4 of the axle 2 to the body of the motor vehicle (indicated 6) about a transverse axis 7. The characteristics of the support 5 will be described in detail below. The axle 2 is further connected to the body 6 by two torque arms 8, each of which has a front end articulated to the body 6 and a rear end articulated to the axle 2 adjacent a respective end part of the latter. The front ends of the two torque arms 8 are aligned on a transverse axis which coincides with the axis 7. The resilient means of the suspension consist of a pair of helical springs interposed between the end parts of the axle and the body. In the drawings, the attachment points of these springs are indicated 9. As can be clearly seen from Figure 1, the suspension described above differs from others of the same type made previously, in that the two torque arms 8 are arranged in two directions which converge towards the rear of the motor vehicle. Moreover, as will be described in greater detail below, the elastic damping support 5 is capable of allowing both small movements of the axle in the transverse direction and small rotations about a vertical axis relative to the body of the motor vehicle. Referring to Figure 3, which shows diagrammatically in plan view a vehicle with rear wheels 3 and front wheels 10 while' it is taking a right-hand bend, the point 0 shows the position of the axis of rotation of the vehicle, through which the axes 3a, 3b, and 10a, 10b of the wheels 3, 10 should pass in theory, precisely as shown in the drawing. It is known in fact that, as a result of errors due to the steering connections, the prolongations of the axes of the front and rear wheels do not generally encounter the axis of rotation of the vehicle. In this case, the motion of each wheel results from a rolling movement and a displacement in the transverse direction, the transverse displacement being able to occur without any clear effect of slipping in contact with the ground due to deformation of the tyres. During the steering manoeuvre, the transverse acceleration to which the vehicle is subjected causes a corresponding stress which tends to push the axle 2 in the transverse direction relative to the body which is proportional to the road holding forces in the transverse direction in the areas of contact between the tyres of the rear wheels and the ground. In the case of the example shown with reference to a right-hand bend, the axle 2 tends to shift to the right (referring to Figure 1) in relation to the body of the motor vehicle. As shown in Figure 2, the transverse displacement of the axle 2 to the right, allowed by the support 5, thus causes, due to the particular inclination of the torque arms 8, a clockwise rotation (with reference to the drawings) of the axle by an angle indicated I. This rotation of the axle 2 tends to cause the motor vehicle to turn to the left, that is, to understeer in relation to a turn to the right. Hence, still referring to Figure 3, the axis of rotation of the vehicle shifts from point 0 to point 0' so that the directions of the actual movements of the wheels 10, 3 are those indicated by the arrow B in Figure 3 (perpendicular to the straight-lines joining the wheel centres to the centre of rotation of the vehicle). Theletters C indicate the drift angles of each tyre. Figures 4 to 6 show a preferred embodiment of the support 5 for connecting the central part 4 of the axle to the body of the motor vehicle. It is clear, however, that the elastically-yielding means connecting the axle to the body may be constituted by any other type of mechanical ,hydraulic, pneumatic or electromechanical device and may possibly make use of an electronic control. In the solution shown, the support 5 includes a first anchoring element consisting of a metal bush 11 having its axis 12 directed transversely and being fixed by a bolt 13 to two appendages 14, which project from the central part of the axle 2. The support 5 also includes a second anchoring element 15 including a pair of flanges 16 fixed by bolts 17 to a cross member 18 which forms part of the body of the motor vehicle. Between the first and second anchoring elements 11, 15 there is interposed an intermediate metal element 19. This intermediate metal element 19 is provided with a tubular metal part 20 which coaxially surrounds the metal bush 11. The intermediate element 19 also has two flat side walls 21 parallel to the longitudinal direction of the motor vehicle and so inclined as to define a V in a plane perpendicular to this longitudinal direction. The two walls 21 face two corresponding walls 22 similarly inclined and forming part of the second metazl anchoring element 15. The support 5 includes first elastic damping means comprising an annular body of elastomeric material 23 having its inner and outer surfaces joined respectively to the bush 11 and to the tubular part 20 of the intermediate element 19, and second elastic damping means comprising two small blocks of elastomeric material 24 interposed in a prestressed condition between the two pairs of facing walls 21, 22. The metal intermediate element 19, and the metal anchoring element 15 have two superimposed walls 25, 26 which are in contact with each other in two distinct areas 27 of circular profile. Thus, it is possible to rotate the intermediate element 19 relative to the anchoring element 15 about either one of two longitudinal axes 28 vertically spaced from the axis 12. The two small blocks 24 tend to oppose rotation of the intermediate element 19 about either of the two axes 28 and , moreover, they urge the intermediate element upwards against the corresponding areas of contact with the wall 26 of the anchoring element 15. As can be seen in Figures 5 and 6, the annular elastomeric element 23 has two slots 29 aligned with each other in a substantially longitudinal direction. By virtue of the particular construction and arrangement described above, the support 5 has a number of advantageous characteristics: Rigidity of the support in relation to movements of the central part of the axle 2 in the longitudinal direction will be relatively small (such as to allow movements of the order of 5 - 6 mm) insofar as these movements are permitted by deformation of the annular elastomeric body 23 and this deformation is facilitated by the existed'cue of the sloWs 29. Thus, excessively high stresses in the longitudinal direction are avoided. Rigidity of the support 15 in relation to movements of the central part of the axle 2 in the vertical direction will be high (the parts of the annular elastomeric body 23 above and below the metal bush 11 are in fact without slots) so as to permit correct working of the suspension. Rigidity of the support 15 in relation to rotations of the axle about a longitudinal axis is relatively small. The same applies to rigidity of the support in relation to rotations of the axle about the axis 12. Rigidity of the support 5 in relation to rotations of the axle about a vertical axis (see Figure 2) is high, but nevertheless capable of allowing small amounts of rotation. Finally, regarding the rigidity of the support in relation to movements of the central part of the axle 2 in the transverse direction, this is relatively high (as will be described in detail below) for transverse deformations below a predetermined value but diminishes progressively with an increase in the deformation beyond this predetermined value. Moreover, for the reasons which are explained below, the support 5 possesses lower values of rigidity in the transverse direction upon increases in the loading on the rear axle of the motor vehicle. As shown in Figure 1, the resilient means 9 of the suspen sion are shifted towards the front of the motor vehicle relative to the axis of the rear wheels. From this it follows that for any given loading condition of the motor vehicle, the reaction of the resilient means 9 produces a downward thrust which is transmitted by the central part 4 of the axle 2 to the support 5. More specifically, this downward thrust, which obviously increases with an increase in the load on the rear axle of the motor vehicle,is transmitted by the axle 2 to the intermediate metal element 19 throughtheelastomer body 23. When the axle 2 is subjected to a transverse load F (see Figure 4) as in the case illustrated in Figure 2, a transverse displacement of the central part of the axle occurs initially after deformation of the annular elastomer body 23. The rigidity of this body 23 in relation to movements of this kind is relatively high and, and as already described above, this prevents even small transverse loads, such as those occuring, for example, during travel in a straight line on a motorway due to uneven road surfaces, from causing a transverse displacement of the axle and its consequent rotation in the horizontal plane. When the transverse load F reaches values greater than those which can be absorbed by deformation of the annular elastomeric body 23, such loads tend to cause rotation of the intermediate metal element 19 about one of the two longitudinal axes 28. As described above, the two small blocks 24 thrust the intermediate element 19 against the lower surface of the wall 26. This wall 26 therefore exerts two reaction forces directed downwards corresponding with the twoareas of contact 27. Referring to the example shown in Figure 4, the action of the transverse load F causes a progressive reduction in the reaction force at the area of contact 27 shown on the left. When the reaction force at the area of contact on the,left is nil, the intermediate element 19 rotates about the longitudinal axis 28 on the right, with consequent tangential stress and compression of the small blocks 24. In the graph of Figure 7 of the accompanying drawings, curve 1 shows the forcedisplacement characteristic, still referring to transverse movements of the support 5. As seen from the graph, when the transverse load is less than a value F1, rigidity in the transverse direction is relatively high and consequently displacements are small. For transverse forces above F1 (which is the value corresponding to maximum deformation of the annular elastomeric body 23) the rigidity of the support decreases. Since the downward thrust transmitted from the axle 2 to the intermediate element 19 increases with an increase in the load on the rear axle, the reaction forces transmitted by the wall 26 to the wall 25 in the two areas of contact 27 will consequently be reduced, so that the intermediate element 19 can start to rotate at lower values of the transverse load. From this it follows that the force-displacement curve corresponding to a greater load is shifted downwards, as shown by the line m in Figure 7. Thus, transverse yielding and consequent rotation in the horizontal plane of the rear axle are more marked the higher the load on the rear axis. This means that the understeering effect due to rotation of the axle in the horizontal plane increases with the increase in the load on the rear axis, that is, upon an increase in the tendency of the motor vehicle to oversteer. It is thus possible to see that the vehicle has a substantially uniform behaviour (and, specifically, understeering) whatever its loading condition. The graph of Figure 8 shows the variation of the angular position of the axle in a horizontal plane as a function of the transverse load. The graph of Figure 9, on the other hand, shows the variation in the angle of steering wheel of the motor vehicle as a function of the transverse acceleration for a given radius of curvature. The lines nland n2 relate to a suspension according to the prior art which does not provide for rotation of the axle, in conditions of minimum loading and full loading of the motor vehicle, respectively. As can be seen, when the vehicle is unladen, its behaviour is understeering (the transverse acceleration increases with the increase in the angle of the steering wheel) whereas,when the vehicle is fully loaded, the behaviour of the vehicle is oversteering (the transverse acceleration increases as the angle of the steering wheel decreases). The two lines 1 and P2 show the behaviour of a motor vehicle having a suspension according to the invention in conditions of minimum and full loading. As can be seen, in this case the motor vehicle understeers even under the condition of full-loading and the difference in behaviour with a variation in the load is much less than that occuring in known solutions. Naturally, the principle of the invention remaining the same, the details of construction and forms of embodiment may be varied widely from what has been described and illustrated without thereby going beyond the scope of this invention.

Claims: CLAIMS 1. Suspension for motor vehicles, comprising: an axle (2) carrying two wheels of the motor vehicle at its ends and being shaped substantially as a V disposed in a horizontal plane such that its central part (4) is displaced towards the front of the motor vehicle, elastically-yielding connection means (5) for the articulated connection of the central part of the axle to the body of the motor vehicle about a transverse axis (7), a pair of torque arms (8) each connected at one end to the body of the motor vehicle (6) and at the opposite end to the axle (2) in correspondence with a respective end part of the latter, and resilient means (9) interposed between the end parts of the axle (2) and the body (6) of the motor vehicle, charácterised in that the elastically-yielding connection means (5) are shaped so as to allow both transverse displacements of the central part (4) and its rotation about a vertical axis,and in that the two torque arms (8) are arranged in two directions inclined to a vertical longitudinal plane in such a manner that a transverse displacement of the central part (4) of the axle (2) relative to the body, caused by the transverse acceleration to which the motor vehicle is subjected on a bend, also causes rotation of the axle (2) about a vertical axis in a direction which tends to oppose the steering of the motor vehicle. 2. Suspension according to Claim 1, in which the two torque arms (8) have their front ends aligned on a transverse axis coinciding substantially with the transverse axis (7) of articulation of the axle (2) characterised in that the torque arms (8) are arranged in two directions which converge towards the rear of the motor vehicle. 3. Suspension according to Claim 1, characterised in that, in relation to transverse displacements of the central part of the axle, the elastically-yielding connection means (5) have a relatively high rigidity for deformations below a determined value (F1) and decreasing rigidity as deformation increases beyond the said determined value. 4. Suspension according to Claim 3, characterised in that the elastically-yielding connection means have lower rigidity values in the transverse direction upon increases in the vertical load on the suspension. 5. Suspension according to Claim 4, characterised in that the elastically-yielding connection means are constituted by an elastic support (5) which comprises: a first anchoring element (11) fixed to the central part of the axle, a second anchoring element (15) fixed to the body (6) of the motor vehicle, an intermediate element (19), first elastic means (23) interposed between the intermediate element (19) and the first anchoring element (11), second elastic means (24) interposed between the intermediate element (19) and the second anchoring element, and means for the articulated support of the intermediate element (19) on the second anchoring element (15) about at least one longitudinal axis (28) spaced vertically from the central part (4) of the axle, in which the first elastic means comprise an annular body (23)ofelastcmericmaterial having its axis directed transversely and its inner and outer surfaces joined to the first anchoring element (11) and to the intermediate element (19), in which the second elastic means (24) are so arranged as to oppose any rotation of the intermediate element (19) about the said longitudinal axis (28), in which the resilient means (9) of the suspension are shifted towards the front of the motor vehicle relative to the end parts of the axle (2), whereby the load bearing upon the suspension causes a downward thrust transmitted from the central part (4) of the axle (2) to the elastic support, and in which means are provided to bring about, upon an increase in the vertical load on the suspension, a reduction in the minimum value of the transverse force sufficient to cause a rotation of the intermediate element (19) about the said longitudinal axis. 6. Suspension according to Claim 5, characterised in that the intermediate element (19) and the second anchoring element (15) have two superimposed walls (25, 26) in contact with each other in two distinct areas of contact (27), the wall of the intermediate element (19) being in the lower position, in that the areas of contact (27) are so shaped as to allow the intermediate element (19) to rotate about one area of contact or the other in correspondence with a respective longitudinal axis (28), and in that the second elastic damping means (24) are so arranged as exert two transverse thrusts directed towards one another on the two sizes of the intermediate element (19) so as to oppose rotation of the latter about either of the two areas (27), and a vertical upward thrust, tending to keep the intermediate element (19) and the second anchoring element(15) in contact with each other in correspondence with said areas (27). 7. Suspension according to Claim 6, characterised in that the second elastic means comprise, two small blocks of elastomeric material (27) disposed in two planes inclined like a V in a plane perpendicular to the longitudinal direction of the motor vehicle, each small block (24) being interposed in a prestressed condition between a respective inclined lateral wall (21) of the intermediate element (19) and a wall (22) with an inclination corresponding to the second anchoring element (15). 8. Suspension according to Claim 5, characterised in that the annular body (23) of elastomeric material has at least two diametricÅally opposing slots aligned in a substantially longitudinal direction.

Inventors: MORELLO, LORENZO
Applicants: FIAT AUTO S.P.A.
Application year: 1984
Main classification: B60G9
IPC codes: B60G9