EP1395452A1

EP1395452A1 - Suspension of a pneumatic type with compensation of differences in level and transfer of load

Info

Publication number: EP1395452A1
Application number: EP02741154A
Authority: EP
Inventors: Renato Cesca; Renzo Ferranti; Stefano Musci; Oscar Proietti
Original assignee: Ncm Srl
Current assignee: Ncm Srl
Priority date: 2001-06-06
Filing date: 2002-05-24
Publication date: 2004-03-10
Also published as: ITTO20010547A1; ITTO20010547A0; WO2002098686A1

Abstract

A suspension of a pneumatic type (1), comprising an air spring (6) including a top fixing plate (4), a bottom fixing plate (2), a bellows body (10), of elastically compliant material, extending between the top fixing plate and the bottom fixing plate, a telescopic assembly (8) housed inside the bellows body, and a hydraulic control system (21-23) for controlling extension of the telescopic assembly (8). The hydraulic system includes a tank (23) for an actuator liquid, at least one feed pipe (21) extending between the tank and the telescopic assembly (8), and actuators (22) connected between the tank and the telescopic assembly.

Description

SUSPENSION OF A PNEUMATIC TYPE WITH COMPENSATION OF DIFFERENCES IN LEVEL AND TRANSFER OF LOAD

TECHNICAL FIELD The present invention relates to a suspension of a pneumatic type with compensation of differences in level and transfer of load.

BACKGROUND ART As is known, a suspension is formed by a complex of mechanical members set between the chassis or the body of a vehicle and the road, and comprises a spring, a shock absorber, various moving parts (arms, hub, articulated joints, etc.) and a wheel

(tire and rim) and has the purpose of enabling relative motion between the wheel, which follows the road profile, and the body, at the same time maintaining certain given geometrical schemes and certain given values of the characteristic angles. These values of the characteristic angles are of fundamental importance in determining the dynamic behavior of the vehicle, and by varying them, it is possible to bestow on the vehicle particular forms of behavior when proceeding in a straight line and when curving in order to guarantee comfort (which calls for soft suspensions in order to be able to follow the road properly) and a good road holding (which calls for rigid and properly damped suspensions) . Given that the above two requirements are frequently in contrast with one another, it is necessary to choose a compromise that is linked to the use to which the vehicle is put.

Hereinafter, reference will be made to suspensions equipped with pneumatic or air springs, which are currently preferred to leaf spring for use in heavy vehicles.

In the case of air springs, it is possible to regulate the characteristics of rigidity in a simple way by introducing air under pressure. In addition, air springs provide a much higher level of comfort than other types of springs. Consequently, air springs provide complete freedom of definition of some of the fundamental parameters of the suspension, making possible a constancy of vehicle attitude and variations in height of the center of gravity of the vehicle under different loading conditions .

Compressed air operates, in fact, as an elastic element which is introduced into a containing structure that is defor able by means of one or more compressors, which also have the job of appropriately regulating the internal pressure according to the load.

Notwithstanding the evident advantages of air springs, there exist situations in which they are unable to perform their function satisfactorily and in which there may arise risks of accidents .

In particular, under static conditions, heavy motor vehicles may find themselves working in dangerous situations of attitude on account of delicate operations such as the loading or unloading of goods (for instance, on work sites). In such critical situations, the center of gravity of the vehicle might undergo appreciable variations until the vehicle may even topple over. In these cases, air springs are no longer sufficient to restore correct attitude.

Furthermore, also in dynamic conditions, there may arise situations that are disadvantageous from the standpoint of road holding and comfort, it not being possible to prevent such situations from arising with current suspensions of a pneumatic type. In fact, as a result of the suspensions, the body of the vehicle may shift with respect to the wheels, so performing different movements, among which pitching and rolling caused by transfer of loads, which are all the heavier in the case of heavy motor vehicles. For example, the accelerations and decelerations which arise during motion can cause transfer of load in a longitudinal direction, which brings about a variation in the load weighing on the front and rear axes of the vehicle.

Any transfer of load in a longitudinal direction is of an amount that is all the greater, the greater are the forces generating this transfer of load, the greater is the weight of the vehicle, the higher is the position of the center of gravity and the smaller the length of the wheel base. In addition to affecting comfort, any transfer of load in a longitudinal direction also affects road holding, given that, during braking, lightening of the rear axle limits the braking action. During acceleration, lightening of the load brings about, instead, possible effects of understeering on bends and loss of adherence, which do not enable discharging of all the power available onto the ground on account of skidding of the wheels (in the case of a front-wheel drive) . The motion to which the body is subjected in this case is called pitching and also affects the values of the characteristic angles owing to compression-load deflection or distension of the suspensions, with evident danger in the case where the vehicle is carrying heavy loads.

Similar risks exist in the case of rolling, owing to a transfer of weight in the transverse direction of the vehicle instead of in the longitudinal direction. This may occur, for instance, in the event of entry onto a bend at a high speed, which causes a greater loading on the outside front wheel and a gust of side wind. Such cases of transfer of load in the transverse direction are of an amount that is greater, the greater are the forces causing such transfer of load, the greater the weight of the vehicle, the higher the position of the center of gravity, and the smaller the width of the * track" (axial width) . DISCLOSURE OF INVENTION

The aim of the present invention is to overcome the limitations of known suspensions in order to prevent the critical situations described above from arising and to provide, in addition to the typical functionality of air springs, also a leveling mechanism and/or a mechanism for compensation of any transfer of load occurring in the static regime and in the dynamic regime.

According to the present invention, a suspension of a pneumatic type is provided which comprises an air spring including a bellows body, made of elastically compliant material, characterized by a telescopic assembly housed inside said air spring and control means for controlling extension of said telescopic assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, with reference to the annexed drawings, which illustrate a non-limiting example of embodiment thereof, and in which:

Figure 1 is a cross-section through a suspension according to the invention in an extended position;

Figure 2 is a cross-section through the suspension illustrated in Figure 1, in a retracted position; and Figure 3 illustrates a block diagram for a suspension control system according to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Figures 1 and 2 illustrate a suspension 1 according to the invention. The suspension 1 comprises: a bottom plate 2 for fixing to an axle of a vehicle (not illustrated) by screw means 3 represented schematically; a top plate 4 for fixing to the back of a vehicle by screw means 5 (also represented in a schematic way) ; an air spring 6; a spring-guide cylinder 7; and a telescopic hydraulic assembly 8. The air valve 6 comprises a bellows-type cylindrical body 10 of elasto eric material, fixed with a top end to the top plate 4 and with a bottom end to the telescopic hydraulic assembly 8, together with the spring-guide cylinder 7.

The telescopic hydraulic assembly 8 is made up of: a bottom cylinder 12; an intermediate cylinder 13, telescopically inserted in the bottom cylinder 12; and a stem 14, telescopically inserted in the intermediate cylinder 13. The top end of the stem 14 is connected to the top plate 4 by means of a first ball-and-socket joint 15; the bottom cylinder 12 is closed at the bottom by a base 16 connected to the bottom plate 2 by means of a second ball-and-socket joint 17.

The bottom plate 2 and the base 16 are each traversed by a respective hole 19a, 19b, the two holes being aligned with respect to one another and being designed to house a coupling 20, illustrated only schematically, connected to a delivery and return pipe 21 for supply of oil under pressure from/to a tank/pump assembly 23 under the control of actuators 22 (typically solenoid valves) set in any suitable point of the delivery and return pipe 21, between the suspension 1 and the actuators 22. As an alternative to what is shown, instead of a single delivery and return pipe 21, two distinct pipes, a delivery pipe and a return pipe may be provided, each having own actuators.

The air spring 6 is connected to a system, of a known type, for adjusting the rigidity of the spring, the system being equipped with a compressor (not illustrated) which operates in a traditional way. The air valve 6 is integrated with the telescopic hydraulic assembly 8 according to the invention, which is controlled by the actuators 22 for maintaining the body of the vehicle in an approximately horizontal attitude and/or for maintaining the position of the center of rolling constant with respect to the inertial axis, as described in greater detail hereinafter.

In particular, in case of static operation, for instance, during the stages of unloading (with the vehicle stationary or almost stationary) , when the center of gravity of the vehicle departs frqrn a condition of safety, oil under pressure is fed from the tank/pump assembly 23 by means of the actuators 22 inside the telescopic hydraulic assembly 8 and causes extension of the suspension 1 and stiffening of the air spring 6 . In this way, the necessary distance is guaranteed between the body and the axle for the body to return to the approximately horizontal position. The suspension 1 operates here, in practice, as a leveling mechanism.

Control of the telescopic hydraulic assembly 8 can be obtained, in this case, according to. three different modalities.

A first modality envisages a direct control of the actuators 22 by the operator who, from his driving position in situations of rough terrain that might jeopardize the attitude of the vehicle, controls entry or exit of the oil from the telescopic hydraulic assembly 8 and hence the amount of the extension of the suspension 1 in order to block or restore the attitude.

A second modality envisages an electromechanical servo mechanism in which the actuators 22 are constituted by proportional valves capable of opening and closing for regulating the passage of oil under the control of a system of equalizers that are sensitive to the inclination of the body.

A third modality envisages an electronic control system which, after enabling by the operator, automatically measures the inclination of the body with respect to a position of horizontal attitude and controls the amount of opening/closing of the actuators 22 in an automatic way.

An electronic system of the above type is, for example, illustrated in Figure 3, in which a plurality of suspensions 1 are represented in a schematic form, the suspensions being arranged in a known way on a vehicle between the axles and the body, the corresponding delivery and return pipes 21, the corresponding actuators 22, and the tank/pump assembly 23. The electronic system 40 illustrated in Figure 3 comprises pressure sensors 30 arranged inside each pipe 21 in a position comprised between the suspensions 1 and the corresponding actuators 22, and supplying pressure signals to a control unit 31 (for instance, a microprocessor) via lines 41. Each actuator 22 is connected to the control unit 31 through a first line 42, on which the control unit 31 supplies a control signal to the actuator 22, and a second line 43, on which each actuator 22 supplies to the control unit 31 an operativeness signal in order to enable control of proper operation of the actuators. Position transducers or inclinometers 32 are set in appropriate points of the body of the vehicle and, via respective lines 44, supply position signals to the control unit 31. Finally, the control unit 31 is connected to an interface 33 for exchange of commands and information with an operator by means of an input/output unit (not illustrated) .

In the electronic system 40, on the basis of the level of inclination of the vehicle, measured by position transducers 32, the control unit 31 issues commands to the actuators 22 in order to pressurize the various telescopic hydraulic assemblies 8 of the various suspensions or to de-pressurize the assemblies, so as to restore the horizontal attitude of the body and/or of the loading surface. The control unit 31 moreover verifies proper operation of the electronic system 40 according to the pressure signals supplied on the lines 41 and to the operativeness signals supplied on the lines 43. The information of activation/deactivation of the electronic system 40, as well as any possible operating information (alarms, etc.) are exchanged through the interface 33.

In case of dynamic operation of the suspensions 1, an electronic control system similar to the one illustrated in Figure 3, verifies the existence of pitching conditions, causing a stiffening of the air springs 6 by extending the telescopic hydraulic assemblies 8, in real time, as soon as a displacement of load is detected, so as to prevent any loss of adherence and poor levels of comfort.

Likewise, in the case of rolling, the electronic control system 40 acts automatically so as to fix the reciprocal positions between the inertial axes of the vehicle and the roll axes in order to guarantee stability of attitude when curving at high speed, as well as to prevent dangerous swaying of the body. In particular, in this case, signals are issued to the control unit 31 regarding any inclination of the body of the vehicle, these signals being supplied on the lines 44 by the position transducers 32, and the value of extension of each individual telescopic hydraulic assembly 8 (for example, measured on the basis of the pressure signal supplied by the pressure sensors 30) .

The advantages provided by the suspension described herein are evident from the foregoing description. It is emphasized only that the function of compensation of differences in level and of any transfer of load achieved with the suspension according to the present invention does not modify the characteristics of overall dimensions and applicability of the axle presented by known air suspensions, so that the installation of the suspensions according to the present invention do not involve any additional burdens or complications.

Finally, it is clear that modifications and variations may be made to the suspension described and illustrated herein, as well as to the corresponding control system, without thereby departing from the scope of the present invention.

Claims

1. A suspension of a pneumatic type (1), comprising an air spring (6) including a top fixing plate (4), a bottom fixing plate (2), a bellows body (10), of elastically compliant material, extending between the top fixing plate and the bottom fixing plate, characterized by a telescopic assembly

(8), housed inside said air spring and connected between said top and bottom constraint means (4, 2) and extension-control means (21-23) for controlling extension of said telescopic assembly (8) .

2. The suspension according to Claim 1, characterized in that said extension-control means (21-23) are of a hydraulic type.

3. The suspension according to Claim 1 or 2, characterized in that said top and bottom constraint means comprise a top plate (4) and a bottom plate (2) .

4. The suspension according to Claim 3, characterized in that said telescopic assembly (8) comprises: a bottom cylinder (12) connected to said bottom plate (2); an intermediate cylinder (13) telescopically connected to said bottom cylinder (12); and a stem (14) telescopically connected to said intermediate cylinder (13); said bellows body (10) being fixed, at the top, to said top plate (4) and, at the bottom, to said bottom cylinder (12) ;

5. The suspension according to Claim 3 or 4, characterized in that said telescopic assembly (8) is connected to said top and bottom plates (4, 2) through ball-and-socket joints (15, 17) ;

6. A system for modifying vehicle attitude, characterized in that it comprises a pneumatic suspension (1) according to any of Claims 1-5.

7. The system for modifying vehicle attitude according to Claim 6, characterized by a hydraulic supply system including a tank (23) containing an actuator liquid, at least one feed pipe (21) extending between said tank and said telescopic assembly (8), and actuator means (22) connected between said tank and said telescopic assembly.

8. The system according to Claim 7, characterized in that said actuator means (2) comprise servo valves.

9. The system according to Claim 7 or 8, characterized by a control unit (31) connected to said actuator means.

10. The system according to Claim 9, characterized in that said control unit (31) is connected to an interface unit (33) for exchange of commands and/or information with the outside world.

11. The system according to Claim 9 or 10, characterized in that said control unit (31) comprises an automatic electronic control unit.

12. The system according to Claim 11, characterized by position-transducer means (32) connected to said electronic control unit (31) and supplying inclination signals, and pressure sensors (30) arranged along said feed pipe (21) and supplying pressure signals to said electronic control unit.

13. The system according to Claim 11 or 12, characterized by connection lines (43) extending between said actuator means

(22) and said control unit (31) and supplying a signal for operativeness of said actuator means to said electronic control unit.