The machine for folding motor vehicle air bags has a table (3) and a movable support on a vertical axis (Z-Z) to engage a fixed part of the bag (5). A compacting press (24) moves parallel to the table to the table and radially with respect to the fixed bag section. A press (32A,B) is connected for radial movement with respect to the contacting press between raised and lowered positions. Claims include a method of using the machine
1. Device for folding an airbag for a motor vehicle safety device, comprising a substantially horizontal table (3) to support an empty airbag (1) which is spread out, a maintaining member (17) movable along a substantially vertical axis (Z-Z), between a position of release of the airbag located over the table (3) and a position of support on one part of the airbag (5) defining a fixed part, and a compacting member (24) movable in a direction parallel to the table (3), radial relative to said fixed part (5), so as to be able to carry out a compacting operation of the airbag (1) by displacing it from a peripheral point on the airbag (1) toward the fixed part (5), characterised in that it further comprises at least one pressing member (32A, 32B) connected in radial displacement to the compacting member (24) and movable relative thereto along a substantially vertical axis between an upper position over the table (3) and a lower position of pressure on the airbag (1). 2. Device for folding according to claim 1, Characterised in that said pressing member (32A, 32B) is movable relative to the compacting member (24) with an alternate movement between the upper and lower positions. 3. Device for folding according to claim 1 or 2, characterised in that said pressing member (32A, 32B), in its upper position, is adapted to be released from the airbag (1). 4. Device for folding according to any of claims 1 to 3, characterised in that it comprises two such pressing members (32A, 32B) radially offset. 5. Device for folding according to claim 4, characterised in that said pressing members (32A, 32B) are adapted to be actuated by a relative movement in translation with respect to one another, along their substantially vertical axis of displacement. 6. Device for folding according to any of claims 1 to 5, characterised in that said compacting member (24) is mounted movable in rotation relative to the table (3) about the axis of displacement (Z-Z) of the maintaining member (17), so as to be able successively to adopt a plurality of angular positions relative to said axis (Z-Z), corresponding to a plurality of successive operations to compact the airbag (1) from different peripheral points on the bag. 7. Device for folding according to claim 6, characterised in that it comprises a single radially movable compacting member (24). 8. Device for folding according to any of claims 1 to 7, characterised in that it comprises at least one retaining member (19) movable along a substantially vertical axis between a position of release of the airbag (1) situated over the table (3) and a position of support on one radially external part of the airbag relative to the fixed part (5), defining a retaining part. 9. Device for folding according to claim 8, characterised in that it comprises programmable electronic control and command means for the positioning and displacement of the compacting member (24) and the retaining member (19). 10. Device for folding according to any of claims 1 to 9, characterised in that the table (3) is provided with clips (50) adapted to pass from a retracted position in the table (3) to a protruding position for clamping one part of the folded airbag. 11. Device for folding according to claim 10, characterised in that said clips (50) are movable in translation relative to the table (3) at least partially interdependently with the compacting member (24). 12. Device for folding according to any of claims 1 to 11, characterised in that the compacting member (24) is mounted in a removable manner on a control arm (22). 13. Device for folding according to claim 12, characterised in that said arm (22) is adapted to receive a gripping member (25) to place one part of the housing (40) on the folded airbag. 14. Device for folding according to any of claims 1 to 13, characterised in that it comprises a heating point (3B) in which means (103) for heating the airbag are arranged. 15. Device for folding according to claim 14, characterised in that the table (3) is capable of rotating about a substantially vertical axis, so as to adopt at least two angular positions relative to said axis, one position corresponding to the position of the airbag (1) in the heating point (3B) and the other position corresponding to the position of the fixed part (5) to the right of the maintaining member (17) and to the compacting operations. 16. Device for folding according to claim 15, characterised in that the table (3) is capable of adopting a third angular position relative to said axis, corresponding to a position of free access (3A) which allows an operator (8) or a robot to place and fix an airbag (1) on the table (3). 17. Device for folding according to claim 16, characterised in that it comprises command means for rotating the table (3), adapted to place the table (3) successively in its position of free access (3A), its position for heating the airbag (3B) and its position for compacting the airbag (3C). 18. Device for folding according to any of claims 1 to 17, characterised in that the table (3) is provided with suction means (13) adapted to exert suction forces on the airbag (1) tending to flatten it in places on the table (3). 19. Method for folding an airbag for a motor vehicle safety device, in which the empty airbag (1) which is spread out is placed on a substantially horizontal support table (3) and the airbag (1) is held flattened on the table (3) around a fixed part (5) by exerting pressure on said fixed part (5) of the airbag, characterised in that subsequently the following sequence of successive basic operations is carried out at least twice consecutively, from different peripheral points on the airbag (1); - the airbag (1) is compacted by exerting a substantially horizontal radial pressure toward the fixed part (5), at a peripheral point on the airbag (1), by means of a compacting member (24); and - the part of the bag thus compacted is held by exerting a substantially vertical pressure, by means of a retaining member (19), and in that during the basic compacting operation, pressure is exerted along a substantially vertical axis by means of a pressing member which is connected in radial displacement to the compacting member. 20. Method for folding according to claim 19, characterised in that between two successive basic operations, the compacting member (24) is angularly displaced relative to a substantially vertical axis (Z-Z) passing through the fixed part (5). 21. Method for folding according to claim 19 or 20, characterised in that during the basic compacting operation, alternate pressures are exerted in a substantially vertical direction on the part of the airbag during compacting, so as to form folds. 22. Method for folding according to claim 21, characterised in that said alternate pressures are exerted in at least two radially offset regions of the part of the airbag during compacting. 23. Method for folding according to any of claims 19 to 22, characterised in that a negative pressure is created between the airbag (1) and the support table (3) by suction means (13). 24. Method for folding according to any of claims 19 to 23, characterised in that an operation for heating the airbag is carried out prior to the sequence of basic operations. 25. Method for folding according to any of claims 19 to 24, characterised in that one part of the housing (40) is placed over the folded airbag and the folded airbag is pressed toward the interior of the housing (40) by means of an expelling member (9) with an upwardly vertical movement.