VARIABLE-STIFFNES AIR SPRING, PARTICULARLY FOR MOTOR VEHICLE SUSPENSIONS

Abstract: The spring comprises a flexible tubular casing (1) to the ends of which are connected rigid caps defining therewith an air chamber (4) of variable volume. This air chamber (4) is associated with at least one auxiliary air chamber (7). The latter has an opening (5a) for communication with that of variable volume. The auxiliary chamber (7) defines a sup­ plementary volume which can be subtracted from that of the variable-volume chamber (4). Valve means (6) for controlling the communication between the chambers in a predeter­ mined manner are associated with the communicating open­ ing (5a) between the chambers (4,7).

Description: Variable-stiffness air spring, particularly for motor-vehicle suspensions The present invention relates to an air spring, particularly for vehicle suspensions, of the type comprising a flexible tubular casing to the ends of which are connected rigid caps defining therewith an air chamber of variable volume. The object of the present invention is to provide an air spring of the aforesaid type, which has a simple and robust structure and has a stiffness that is variable under control in a predetermined manner. This object is achieved according to the invention by an air spring of the type specified above, the main characteristic of which lies in the fact that the air chamber is associated with at least one auxiliary air chamber which has an opening for communication with the variable-volume chamber and which defines a supplementary volume subtractable from that of the variable-volume chamber, valve means being provided for controlling the commurication between the chambers through the opening in a predetermined manner. Further characteristics and advantages of the air spring according to the invention will become apparent from the detailed description which follows with reference to the appended drawings provided purely by way of non-limiting example, in which: Figure 1 is a perspective view of an air spring according to the invention, Figure 2 is a sectional view taken along the line II-II of Figure 1, Figures 3 and 4 are partially-sectioned views of two variants of the spring shown in Figure 2, and Figure 5 is a sectional view of a further variant of the spring according to the invention, Figure 1 shows an air spring comprising a flexible tubular casing 1, for example of rubberised canvas, with rigid caps 2, 3 connected to its ends in known manner. The casing 1 and the caps 2, 3 define in their entirety an air-filled chamber 4 of variable volume. Referring to Figure 2, a rigid body 5 in the form of an inverted beaker is welded to the lower cap 3 within the chamber 4. The axial dimension of this rigid body 5 is considerably less than the distance between the caps 2, 3. The lower cap 3 and the wall of the body 5 define in their entirety an auxiliary chamber 7 of fixed volume. The wall of the rigid body 5 facing the upper cap 2 has an opening 5a within which is fixed a known type of solenoid valve 6 which controls the communication between the chambers 4 and 7. The solenoid valve 6 is controlled through a connection cable 8 which emerges from the air spring, for example through a sealing connector 9 fixed in a corresponding ready-made hole in the lower cap 3. The solenoid valve 6 is normally kept in a state in which it allows communication between the chambers 4 and 7. In this condition, the volume of compressible air consists in practice of all the air in the casing 1 and thus includes the volume of air within the chamber 7. The spring described above can be used for vehicle suspensions. In this application, when the vehicle meets a bend at high speed, the solenoid valve is closed in order to limit rolling. In this condition, only the volume of air outside the rigid casing 5 is "working" and the stiffness of the air spring is increased. The solenoid valve 6, which can be of the on-off type or the variable-throughput type, is appropriately piloted by a sensor 10, for example a sensor of the transverse acceleration of the vehicle, an inertial sensor, or some other. Figures 3 and 4 show variants in each of which is provided a plurality of auxiliary chambers, indicated 17 in Figure 3 and 27a and 27b in Figure 4. In the variant illustrated in Figure 3, the region within the rigid body 5 is divided into two chambers 17 which do not communicate with one another but communicate with the variable-volume chamber 4 through respective openings 15a controlled by respective solenoid valves 16. In this variant, it is possible to achieve progressive stiffening of the air spring by the successive closure of the two solenoid valves 16. It is therefore possible to achieve a progressive stiffening with the use of very simple and cheap solenoid valves of the on-off type. In the variant shown in Figure 4, the region within the rigid body 5 is divided into two chambers 27a and 27b by an internal transverse partition 12 with an opening 12a. The lower chamber 27a can be put into communication with the upper chamber 27b through an opening 12a in the partition 12, controlled by a solenoid valve 16. The upper chamber 27b communicates in its turn with the variable-volume chamber 4 through the opening 5a in the rigid body 5, which is also controlled by a solenoid valve 16. In this variant, the progressive stiffening of the air spring can be achieved firstly by the closure of the solenoid valve associated with the opening 12a and then by the subsequent closure of the solenoid valve associated with the opening 5a. In the case of the variants shown in Figures 3 and 4 also, the solenoid valves can be piloted by the sensors able to detect, for example, the transverse acceleration of a motor vehicle. Figure 5 illustrates a variant of the spring according to the invention, which can also act as a damper and has a stiffness in compression stages different from the stiffness in extension stages. In this drawing, the parts already described above with reference to the other variants have been given the same reference numerals. In the variant of Figure 5, the rigid body 5 has a central opening 5a at its upper end, to the edge of which a hollow rigid body 36 is sealingly connected. This hollow body has, for example, a cylindrical shape and has through-holes 36a in its side wall which put the interior of the hollow body into communication with the region or 'chamber 7 defined by the casing 5 and the lower cap 3. The wall of the hollow body 36 facing the upper cap 2 has a pair of holes 36b, 36c the second of which has a larger diameter. A ball 38 biassed by a spring 39 into engagement with the lower edge of the hole 36c is located within the hollow body 36.The ball 39 acts as a shutter while the lower edge of the hole 36c acts as a valve seat. The spring 39 reacts at its lower end against the lower wall of the hollow body 36. The variable-volume chamber 4 is in permanent communication with the fixed-volume chamber 7 through the holes 36b and 36a of the hollow body 36. When the spring is compressed during use, the increase of air pressure in the variable-volume chamber 4 pushes the ball 38 downwards against the action of the biassing spring 39 and opens the hole 36c.In this manner, the resistance to the flow of air from the chamber 4 to the chamber 7 will be reduced considerably. When the air spring extends again, the spring 39 urges the ball 38 back into engagement with the hole 36c, and the flow cross-section of the communication between the chambers 7 and 4 is reduced to the section of the one hole 36b. The resistance to the drawing of air from the chamber 7 to the chamber 4 will therefore be greater than for the drawing under compression. Preferably, the cross-section of the hole 36b is much smaller than the hole 36c. By the appropriate selection of the diameters of the holes 36b and 36c,as well as the stiffness of the biassing spring 39, it is possible to produce air springs with stiffnesses and damping characteristics which are different under compression and extension over a wide range of values. The air spring described above can also be used as a damper.

Claims: CLAIMS 1. Air spring, particularly for motor vehicle suspensions, comprising a flexible tubular casing (1) to the ends of which are connected rigid caps (2,3) defining therewith an air chamber (4) of variable volume, characterised in that the chamber (4) is associated with at least one auxiliary chamber (7; 17; 27a, 27b) which has an opening (5a; 15a) for communication with the variable-volume chamber (4) and which defines a supplementary volume subtractable from that of the variable-volume chamber (4), valve means (16) being provided for controlling the communication between the chambers (4; 7, 17, 27a, 27b) through the opening (5a; 15a) in a predetermined manner. 2. Variable-stiffness air spring according to Claim 1, characterised in that the auxiliary chamber (7; 17; 27 , 27b) is formed within the variable-volume chamber (4). 3. Variable-stiffness air spring according to Claim 2, characterised in that the auxiliary chamber (7; 17; 27a, 27b) is adjacent one of the end caps (2; 3). 4. Variable-stiffness air spring according to Claim 3, characterised in that the auxiliary chamber (7; 17; 27, 27b) is constituted by a rigid casing (5) connected to one of the end caps (3). 5. Variable-stiffness air spring according to any one of the preceding claims, characterised in that the valve means comprise at least one solenoid valve (6; 16). 6. Variable-stiffness air spring according to Claim 5, characterised in that the solenoid valve (6;16) is of the on-off type. 7. Variable-stiffness air spring according to Claim 5, characterised in that the solenoid valve (6; 16) is of the variable-throughput type. 8. Variable-stiffness air spring according to any one of the preceding claims, characterised in that a plurality of auxiliary chambers (27a; 27b) are associated with the variable-volume chamber (4), which communicate with each other through openings (12a) controlled by respective valve means (16) so as to define a plurality of supplementary volumes addable to that of the variable-volume chamber (4). 9. Variable-stiffness air spring according to any one of the preceding claims, characterised in that the valve means are controlled in dependonce on signals output by means (10) for sensing the transverse acceleration of the vehicle. 10. Variable-stiffness air spring according to any one of the Claims 1 to 4, characterised in that it further includes valve means (38, 29) for automatically varying the section of the passage (36b, 36c, 36a) between the chambers (4, 7) in such a way that the section of the passage is automatically increased when the air spring is compressed and reduced when the air spring is extended. 11. Variable-stiffness air spring according to Claim 10, characterised in that the communication passage comprises a first hole (36b) which is permanently open and a second hole (36c) with which the valve means (38, 39) are associated. 12. Variable-stiffness air spring according to Claim 11, characterised in that the first hole (36b) has a smaller diameter than the second hole (36c). 13. Variable-stiffness air spring according to Claim 11 or 12, characterised in that the valve means comprise a shutter valve (38) movable under the action of a spring (39).

Inventors: DI GIUSTO, NEVIO, MANNINA, ANTONINO, TREBBI, GIORGIO, VISCONTI, AMEDEO
Applicants: FIAT AUTO S.P.A.
Application year: 1985
Main classification: B60G11
IPC codes: F16F9, B60G11, B60G17