EP2102021A1

EP2102021A1 - Suspension system for a vehicle

Info

Publication number: EP2102021A1
Application number: EP06841627A
Authority: EP
Inventors: Mauro Bianchi
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-12-27
Filing date: 2006-12-27
Publication date: 2009-09-23
Also published as: WO2008080433A1

Abstract

Suspension system for a quadricycle vehicle having at least two front seats, comprising a suspension device for each wheel of the vehicle, each device being provided with elastic elements in compression phase (C) and elastic elements in relaxed phase having very different values and a relaxed stiffness higher than that of the elastic elements in compression phase (C), characterized in that the changing point between the compression phase (C) and the relaxed phase is located at the static position of the vehicle in driving mode with an empty fuel tank and a mass load between 67 kg and 83 kg on each of the front seats.

Description

"Suspension set for a vehicle"

The present invention relates to a suspension assembly for a quadricycle vehicle.

The invention also relates to a vehicle equipped with such a suspension assembly.

It will find its application particularly in the automotive field for the production of suspension members for each wheel of the vehicle in line with operating parameters and in particular predetermined stiffness parameters.

The present applicant is already at the origin of fundamental advances in the field of suspensions. In particular, the so-called CONTRACTIVE principle (registered trademark) of the same applicant is a suspension with two distinct stiffnesses which articulate around the static position of the vehicle with a compression phase and a relaxation phase. According to this principle developed in particular in the document WO-A-91/04876, the stiffness of the suspension in the expansion stroke is significantly greater than that of the suspension in compression stroke with a ratio of the order of 1 to 3. Connection flexibility is also inserted between the linear stiffness zone of the expansion phase and the compression phase so as to avoid a too abrupt passage between the two.

WO-91/04876 shows an example embodiment. An alternative is presented for example in WO-98/26193. This suspension principle has already shown its effectiveness to greatly reduce the importance or eliminate the anti roll bars generally used with conventional suspensions.

However, it turns out that this type of suspension must meet very specific operating parameters to give full satisfaction. In particular, the point corresponding to the change between the two work phases of the suspension (compression and expansion) which is in the static position of the vehicle must be determined accurately to create a self-stabilizing operating reference point.

A poor positioning of this tipping point could seriously degrade the handling and / or the comfort of the vehicle, being reminded that the CONTRACTIVE suspension implements a strong variation of stiffness between the relaxation and the compression.

The aforementioned patent publications call for "a change of stiffness in the static position of the vehicle". The development and various achievements made over several years of activity have demonstrated the existence of two difficulties:

- First, there are practically as many definitions of "the static position of a vehicle" as there are constructors; the definition of "the static position of a vehicle" goes - according to the manufacturer concerned - from the "absolutely empty vehicle" to the definition "with a load corresponding to 4 persons of 80 kg on the seats + 40 kg in the boot"! The difference of these definitions induces a considerable variation of attitude which irreparably damages the good behavior of the vehicle; indeed, the change of stiffness according to a definition of static position corresponding to "empty vehicle" would induce a too degraded attitude plate once the vehicle loaded. On the other hand, a definition of static position corresponding to "with a load corresponding to 4 persons of 80 kg on the seats + 40 kg in the trunk" would induce an unacceptable comfort when the vehicle will be loaded with only one person and the empty trunk.

- Second, like a vehicle equipped with conventional suspensions with anti-roll bars, a vehicle equipped with "Contractive" suspensions will suffer a degradation of its attitude when the vehicle is heavily loaded; to avoid having to resort to more complex and expensive techniques - such as attitude correction or, for the Contractive technique, to a "load-controlled preload" - and to allow operation in accordance with the acceptance of all the manufacturers, a very heavy development was necessary to lead to a definition of the "theoretical static position Contractive" that can be applied to all vehicles.

The object of the invention is, among other considerations, to define very precisely a theoretical contractive theoretical position which will make it possible to very precisely fix the tilt point of the stiffnesses. In addition to the precise definition of this tipping point, the applicant has also, after much work, found that other parameters had to be fixed precisely including Δ stiffness, the importance of the connection stiffness zone, and stiffness clean of the elements including the levitation spring. The applicant thus noted with surprise that the tipping point between the compression phase and the expansion phase had to be at a completely theoretical level, since it was non-rolling and with unusual operating parameters, namely a reservoir of empty fuel and a load between 67 and 83 kilos on each of the front seats of the vehicle.

Although it is a non-rolling configuration, it is by positioning the tilt point of the stiffnesses in accordance with this theoretical static position that the best results will be obtained. As we have seen above, this result is all the more surprising that one could legitimately fear a deterioration of the attitude of trim during a strong load variation especially on the rear axle.

However, according to parameters developed according to the present invention, the degradation resulting from a loading variation on the above suspension proposed remains very contained and is not greater than the degradation observed with conventional suspensions on the same vehicle.

Other objects and advantages will become apparent from the description which follows, which presents a preferred embodiment of the invention, which is however non-limiting.

Before, it is recalled that the invention relates to a suspension assembly for a quadricycle vehicle with at least two front seats comprising a suspension device for each wheel of the vehicle,

Suspension assembly for a quadricycle vehicle having at least two front seats, comprising a suspension device for each wheel of the vehicle, each device being provided with elastic elements in the compression phase (C) and elastic elements in the expansion phase of very different values with a relaxation stiffness greater than that of the elastic elements in the compression phase (C), characterized in that the point of tilting between the compression phase (C) and the expansion phase (DL +

RP) is located at the static position of the vehicle in running order with an empty fuel tank and a mass load of between 67 kg and 83 kg on each front seat.

According to preferred variants further improving the result obtained for all the suspensions, this set is such that:

the suspension devices have, in the expansion phase, a zone of linear stiffness and a zone of stiffness of connection, of low and very progressive stiffness situated between the zone of linear stiffness and the point of tilting. - The connection stiffness zone is between 25% and 45% of the entire stroke of the relaxation phase.

- The zone of connection stiffness is between 30% and 40% of the entire stroke of the relaxation phase. each device comprises elastic elements in compression phase provided with a lift spring configured to produce a natural oscillation frequency of the vehicle suspensions between 1.25 and 1.50 Hertz for the wheels of the front axle. each device comprises elastic elements in the compression phase with a lift spring configured to have a natural oscillation frequency at the static position of the vehicle between 1.25 and 1.75 Hertz for the wheels of the axle back.

- The stiffness ratio between the linear zone of the relaxation phase and that corresponding to the lift phase is between 3.2 and 3.7 for the wheels of the front axle.

- The stiffness ratio between the linear zone of the expansion phase and that corresponding to the lift phase is between 3.0 and 3.5 for the wheels of the rear axle. The invention also relates to a vehicle equipped with a suspension assembly according to the invention.

The accompanying drawings are given by way of example and are not limiting of the invention. They represent only one embodiment of the invention and will make it easy to understand. Figure 1 shows schematically different operating phases of the suspension of the invention with a stroke / force curve on the suspension arm of a wheel.

Curve 1 shows the behavior of a suspension of the type of the invention and curve 2 shows a conventional suspension behavior. Figure 1 also illustrates the stiffness variations schematically with a pair of springs.

FIG. 2 illustrates a load / displacement curve of a suspension according to the invention and FIG. 3 more precisely shows a displacement / load stiffness curve for the progressive connection zone (RP). The suspension element according to the invention means all the suspension devices necessary for the equipment of a vehicle of the quadricycle type having at least two front seats. Generally, the invention will apply to vehicles having front seats and also rear seats.

The suspension element of the invention therefore comprises four suspension devices (one per wheel), each of the devices being provided with elastic elements in the compression phase and elastic elements in the expansion phase with a stiffness in the phase of greater relaxation than that of the compression phase.

According to the invention, the tilting point between the compression phase C and the expansion phase (DL + RP) is located at a theoretical and non-rolling position around the static position of the vehicle in running order defined according to the invention by a vehicle with an empty fuel tank and a load of between 65 and 83 kilograms on each of the front seats.

A mass of 75 kilos on each seat is preferred. This tipping point makes it possible to determine the zone of tilting of the stiffnesses between the two phases of operation of the suspension. This zone of tilt stiffness is marked 5 in Figure 1. It is found that, in the expansion phase, the suspension behaves as a main spring 3 relaxed with, in parallel, a compression of an additional spring 4 of greater stiffness.

A connection stop BR is positioned to be biased in series with the additional spring; its action, with its very gradual and asymptotic stiffness, as illustrated in the example of stiffness provided by FIG. 3, very gradually modifies the stiffness in the expansion phase until the total compression of the abutment BR thus reaching, at the end of the connection phase, the linear expansion stiffness.

The assembly is balanced at the level of the tilting zone 5 corresponding to the theoretical static vehicle position previously defined. Beyond this position, corresponding to the theoretical static position of the Contractive, the spring 3 is compressed while the additional spring 4 is released. The three phases of operation of the suspension are thus obtained, namely an expansion phase, a compression phase and an intermediate transmission phase with connection flexibility.

The schematic illustration given in Figure 1 is of course not limited to industrial achievements that can be conceived.

According to the invention, the transition zone is located entirely in the very first part of the expansion phase as shown in FIG.

In this context, the expansion phase comprises a linear stiffness zone DL and a connection stiffness zone RP for achieving an intermediate flexibility softening the transition and the switching between relaxation and compression. A connection abutment BR is visible in FIG. 1. Advantageously, it has been found that the zone of connection stiffness RP must cover between 25 and 45% of the stroke of the relaxation phase depending on whether a sporty behavior or a behavior will be sought. promoting more comfort.

More precisely, the best results have been obtained with a connection phase of between 30% and 40% of the total relaxation stroke.

Another major point of improvement of the existing CONTRACTIVE suspension is given by the present invention with a selection of stiffnesses for each of the suspension devices.

More precisely, it selects stiffness levitation precisely but with room for maneuver according to the specifications of the vehicle and whether will be sought more comfort or a more sporty temperament.

The stiffness selection range for the compression phase of the front axle is that which will correspond to the values producing oscillation frequencies of the suspensions between 1.25 hz and 1.50 hz depending on whether a behavior promoting greater comfort or sporty behavior.

This interval gives complete satisfaction for the wheels of the front axle and also for the wheels of the rear axle. The frequency of the rear axle will be chosen by those skilled in the art taking into account the following criteria: the raising of the oscillation frequency level of the rear axle will produce a more incisive behavior of the front axle , will provide increased traction for vehicles with front-wheel drive, and finally, for vehicles that are likely to experience high load variations on the rear axle, it will help balance the oscillation frequencies with the fully loaded vehicle .

For the rear axle, however, it may be necessary to vary the stiffness more importantly depending on whether one is dealing with a two-seater coupe type vehicle with little or no variation of the loads on the axle rear, a large sedan-type drive or a four-wheel drive vehicle whose load variation on the rear axle compared to the very large mass of the vehicle will not be very significant; in these latter cases we can opt for an iso- frequency equilibrium. On the other hand, if we consider a vehicle with a much smaller mass and whose load variation on the rear axle can be comparatively much greater, in this case, we can increase the frequency of the rear axle so that this remains more balanced and of the same order as that adopted for the front axle with the full load of the vehicle.

On the other hand, to increase the traction of traction vehicles, or to increase the reactivity of the front axle, one can choose to increase the oscillation frequency of the lift springs of the rear axle. It was found that for the rear axle, the oscillation stiffness could be between 1.25 hertz and 1.75 hertz.

The equation for determining the natural oscillation frequency of the suspension in the compression phase as a function of the mass applied to the wheel and the stiffness of the spring element is described below:

2TJ VMF = oscillation frequency in hertz K = stiffness in newtons / meter M = mass in kilos

In order to comply with the CONTRACTIVE suspension operating criterion developed in the applicant's previous patents (in particular the aforementioned applications WO-91/04876 and WO-98/26193), a stiffness ratio between the linear zone DL of the relaxation phase and the levitation spring element greater than 3.

However, the 15 years of development of the CONTTRACTIVE suspension have shown that the best results were obtained with a ratio for the wheels of the front axle between 3.2 and 3J _j reports considered at the level of the elements, this which takes into account the drifts due to the parasitic flexibilities existing in the suspensions and also to the drift due to the flexibility of connection and between 3 and 3.5 still to the element for the wheels of the rear axle. The parameters determined above allow the realization of a suspension assembly operating without anti-roll bars for a vehicle combining both high handling efficiency with a high level of comfort.

Claims

1. A suspension assembly for a quadricycle vehicle having at least two front seats, comprising a suspension device for each wheel of the vehicle, each device being provided with elastic elements in the compression phase (C) and elastic elements in phase relaxation of very different values with a relaxation stiffness greater than that of the elastic elements in the compression phase (C), characterized in that the point of tilting between the compression phase (C) and the expansion phase (DL + RP ) is located at the static position of the vehicle in running order with an empty fuel tank and a mass load of between 67 kg and 83 kg on each front seat.

2. suspension assembly according to claim 1 wherein the suspension devices have in the expansion phase a linear stiffness zone (DL) and a connection stiffness zone (RP), progressive lower stiffness located between the linear stiffness zone (DL) and the tipping point.

3. suspension assembly according to claim 2 wherein the zone of stiffness connection (RP) is between 25% and 45% of the entire stroke of the expansion phase.

4. suspension assembly according to claim 2 wherein the zone of stiffness connection (RP) is between 30% and 40% of the entire stroke of the expansion phase.

5. An assembly according to any one of claims 2 to 4 wherein each device comprises compression-elastic elements (C) provided with a levitation spring configured to produce a natural oscillation frequency of the vehicle suspensions between 1, 25 and 1, 50 Hertz for the wheels of the front axle.

6. The assembly of claim 5 wherein each device comprises elastic elements in the compression phase (C) provided with a lift spring configured to have a natural oscillation frequency of the vehicle suspensions between 1.25 and 1, 75 Hertz for the wheels of the rear axle.

7. The assembly of claim 5 or 6 wherein the stiffness ratio at the element between the linear stiffness zone (DL) of the expansion phase and that corresponding to the lift spring or the compression phase is between 3.2 and 3.7 for the wheels of the front axle.

8. The assembly of claim 7 wherein the stiffness ratio at the element between the linear stiffness zone (DL) of the expansion phase and that corresponding to the levitation spring or the compression phase is between 3, 0 and 3.5 for the wheels of the rear axle.

9. Vehicle incorporating a suspension assembly according to any one of claims 1 to 8.