Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication
Reexamination Certificate
2002-01-09
2004-02-10
Beaulieu, Yonel (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Reexamination Certificate
active
06691002
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a method for predicting the acoustic and vibratory levels inside a vehicle rolling over ground that has several obstacles or ground of a given particle texture.
The discomfort perceived by the driver and passengers of a vehicle rolling over one or many obstacles (such as manholes, bitumen seams, various joints, gravel, etc.) has two distinct aspects. A first aspect is vibratory and is manifested as vibrations of the vehicle floor, the seats and the steering wheel. A second aspect is acoustic and is manifested as noise produced inside the vehicle by the vibrations of various parts of the vehicle. The discomfort level felt by the occupants of a vehicle depends greatly on the body, the mechanical system through which it is in contact with the ground, the rolling speed and of course the type of obstacle on the road.
Definition of the terms used in what follows:
the “comfort performance” corresponds to the acoustic and/or vibratory level that can be measured inside a vehicle rolling on a road (or a test bed) provided with at least one obstacle of given dimensions;
“suspension system”: the group of vehicle elements that provide the link between one or more contact surfaces between the vehicle and the ground and one or more points of the said vehicle; in all cases the suspension system comprises at least one tire and the wheel to which it is fitted;
“body”: the group of vehicle elements complementary to the suspension system;
“attachment points”: points connecting the suspension system with the body;
“overall transfer finction”: a function comprising two parts, a first part concerning the noise in the cabin of the vehicle and a second part concerning the vibrations at certain predetermined points in the said cabin;
“reference suspension system”: suspension system fitted to the vehicle and available for obtaining the overall transfer function;
“prototype suspension system”: suspension system whose effect on the comfort performance of the same vehicle fitted with the said prototype system in place of the reference system one is seeking to predict, without having the said vehicle available.
For example, a suspension system may consist of a tire and the wheel to which it is fitted: in this case, the point of attachment is the hub. The overall transfer function makes it possible to reproduce the vibration levels inside the body of a vehicle from the forces measured at the hub.
Several methods are known to those familiar with the field for evaluating the comfort performance of a new suspension system for a given vehicle, which make it possible to optimize the said suspension system, such optimization consisting in obtaining characteristics of a contact system that procure an appreciably improved comfort level.
For example, to evaluate and optimize the comfort performance of a vehicle fitted with a new suspension system, a person familiar with the field can use an experimental method involving measurements of the noise and vibrations in the cabin of a vehicle rolling on a section of road or track that produces some vibratory and/or acoustic discomfort in the said vehicle, this section of road or track having one or more obstacles on its surface. However, this method entails availability of the vehicle so that various suspension systems can be evaluated; besides, it can only be carried out in suitable weather conditions and this means that the vehicle is immobilized for times which are sometimes excessively long and consequently lead to excess costs during the development phase of a suspension system since several iterations are often needed. In addition, the method is long and fastidious for the operator and is subject to wide scatter of the measurements.
Furthermore, European Patent Application No. 886130 describes a method of predicting the noise level in the cabin of a vehicle fitted with tires and rolling over uneven ground that has numerous rough points. According to this method, a transfer function is determined for a vehicle fitted with tires by applying, directly to each axle (at the hub) of the vehicle at rest, forces (in the form of shocks) directed in predetermined directions. For each impact a sound recording is made inside the said vehicle and this operation is repeated successively for each of the front and rear positions and on each side of the vehicle. In another stage, an identical tire rolls on a roller track provided on its rolling surface with numerous rough points to simulate uneven ground. In this test, the tire is mounted on a fixed axle and the resultant forces acting at the hub are recorded. Finally, these measured resultant forces are used as input for a model involving the transfer function determined as described earlier so as to obtain the resultant noise level inside the vehicle. This method however, which is certainly interesting, has limitations which, for example with tires of the same size but having different structures, can give noise levels different from those obtained from tests carried out using the same vehicle fitted with these different tires and rolling on uneven ground.
In particular, since the transfer function of the vehicle is established from tests carried out at rest, it is clear that no account is taken of the mechanical characteristics of the tires when rolling, which as a general rule are appreciably different from the same characteristics at rest. Notably, it is known that the vertical rigidity of a tire at rest under dynamic loading is higher than the same vertical rigidity under dynamic loading when the tire is rolling.
Besides, to apply forces at the level of the axles it is necessary to provide an added, fixed component on the outside of the wheel, the said component being designed to receive, for example, blows from a hammer, and it is clear that the mass of the said component is added to the un-sprung weight and so perturbs the measurements made. It must also be pointed out that the noise of each hammer blow, even though means are adopted to attenuate it, is transmitted through the air into the cabin and is at least partly added to the noise one is trying to record inside the vehicle.
The object of the invention is a method of predicting the comfort performance of a vehicle fitted with a suspension system, which does not suffer from the drawbacks of the methods just described.
To achieve this, a method is proposed for predicting the noise and vibrations in the cabin of a vehicle fitted with a prototype suspension system, when the said vehicle is rolling at a given speed V on ground having at least one obstacle of predetermined size.
BRIEF SUMMARY OF THE INVENTION
The method proposed comprises a first stage in which an overall transfer function is determined for the vehicle fitted with a reference suspension system, and a second stage in which forces are measured at the attachment points between the body and the prototype suspension system. Then, the method according to the invention consists in multiplying this overall transfer function of the vehicle obtained in the first stage by the resultant forces acting at the attachment points between the body and the prototype suspension system, when the said prototype suspension system is bearing on its contact surfaces with the ground the same loads as those measured when the vehicle is rolling on the same ground provided with the same obstacle(s).
The overall transfer function is determined by using a series of measurements on the vehicle fitted with a reference suspension system combined with a series of measurements on this reference suspension system attached to a frame at the body attachment points whereby it is fitted to a vehicle. In the case when the suspension system is reduced to the tire and the wheel, the frame is equipped with means that enable the measurement of forces acting at the hub.
The measurements on the vehicle comprise the following stages:
a) the vehicle is fitted with the reference suspension system, the said system being connected to the said vehicle by attachment points;
b) inside the vehicle are arranged means
Dormegnie Eric
Fabry Pierre
Fraysse Patrice
Beaulieu Yonel
Crecente Christopher
Csontos Alan A.
Farley Felipe J.
Michelin & Recherche et Technique S.A.
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